I'll say this over and over

The idea that you can't mix different brands of track is ridiculous. All it takes is some care when making the joints and soldering the joiners. You can even mix codes if you want although there may be some shimming involved sometimes. I'm happy to hear Atlas appearance is improving but I honestly pay more attention to ease of use than appearance when it comes to selecting track, and for me, Atlas code 83 flex and Peco code 83 turnouts win that battle hands down.

On my module I have two Peco code 83 turnouts separated by about a two inch long piece of Atlas code 83. That's four rail joints very close together. I assembled that stretch on my bench paying close attention to rail alignment when I soldered the joints. It's as smooth as silk.

Rail profiles

You shouldn't mix rail profiles more than needed. If you built one section with one profile and need to build another with a different profile, make a minimal number of joints in-between.

It appears that you could get away with mixing ME and Peco though.

Rail Profiles

From the picture it looks like there could be four different manufacturers of rail. So the question is do the companies shown form their own rail or is it bought in stock rolls? If bought in stock rolls, could there be four different companies making rail? Questions I'd like to have answers to, but might be hard to get.

Bernd

Top inside of the rails

( at proper gauge) is all you need to match. As Michael says it isn't a problem. My last O scale layout had areas of code 148, code 125, and code 100 on plastic flex tries and hand spiked on wooden all joined with no problems. It was covered in model railroading 101   :> )  .....DaveB

Mixing

I’ve mixed rail profiles and sizes with no problem.  You can’t just slap some rail joiners on and shove them together, you do need to take a little care to line up the top and guage face as Dave says.  When going from ME rail to Atlas rail you may need to do a little filing to transition from the more rounded inside corner of ME to the square inside corner of Atlas.  It’s not rocket science, it just take a time and effort.  If you do it right, there is no performance penalty, no increased likelyhood of derailment.  There is however a time and effort penalty.  If you stick with a single rail size and manufacturer you’ll save time and effort.

I’m very curious if Atlas has improved their rail profile recently.  Their older wide flat head with sharp corners isn’t great.

  "I’m very curious if Atlas

I'm using code 100 rail on my S scale layout. I have some code 100 shinohara track, some code 100 flex track marketed  by Tomalco that is made by Micro engineering and hand laid turnouts made with code 100 rail stripped from old Atlas flextrack . I haven't noticed any significant difference between them when making joints. I'll see if i can tell any difference in a close up shot. The trains don't seem to mind the difference as they run happily over the line :> ) .....DaveB

To me, its not just about the rail profile …

The ties and spike/plate details are also a big (bigger?) factor, and this is where ME really shines.  Seemingly just slightly random tie placement, just like the real thing.  Very real looking. 

This is ME Code 70 from the side:

 

The slight taper on the ties likely due to their molds, but also good for anchoring in ballast.

The others all look too perfect.  Walthers does a decent job with their spikes on their Code 83 though.

I had planned on using the 8’ 6” Central Valley Tie Strip, but I didn't notice in their website pics these ghastly rail anchor protrusions every 5 ties.  I really can’t stand them, even pushed over, and removing them is very difficult on the web side.  I’ve got two bags them.  I love the look and randomness of the ties, and the spike and plate detail is very fine, but these anchor things just don't do it for me.  

 

Below, I have been trying to cut them off.  It’s easy on the non web side, but hard on the web side.  A chisel blade makes a nice “straight down” removal, but its to easy to accidentally cut through the web on the other side.

 

Even pushed over, they are quite visible (below).  I’ve asked CV about what they were thinking but no reply.  In my view, the suggestion that bending the anchors and spikes over with a nail set is rather bogus as they seem to do nothing fir a mechanical attachment.   I may try and ballast a short section with just the tops of the anchors shaved off as that is easy, and see if ballast and paint, etc., hides them well enough.

 

I bought 6 bundles of ME Code 70 flex yesterday, so I’d have it.  It’s a perfect height match for the CVT Turnout bases used with Proto:87 “Fast and Easy” turnouts.  I’m not sure yet how well they line up vertically with the wood ties used under the Proto:87 ultimate turnouts.

Per other comments here, mechanically, I can’t see any issues mixing brands so long as the inside and top rail web joins are kept smooth through alignment while soldering and/ or careful filing and shimming for height.  Its not like the wheels running through them know the difference.  

Any of today’s flex track is frankly, awesome compared to what we had when I was a kid.  I remember saving paper route money to buy tru-scale roadbed!  I just consider track to be the ultimate foreground scenery.  I’m eventually going to try laying some Proto:87 Ultimate track using their fixtures, tie plates and wood ties with ME Code 70 rail, but haven’t gotten around to ordering as yet.  Andrew mentioned that he has an independent supply of rail so the ME situation isn’t an issue for him one way or the other.

Here is a side-by-side comparison of several brands of track:

Left to right:

• Atlas Code 83 True-Track
• Central Valley 2001 9’ Tie Strip with ME Code 70 weathered rail - this has awesome detail and is comparable to flex track in its perfect straightness. 
• ME Code 70 Flex-Track
• PECO Code 83 Flex Track
• Central Valley 2003 8’6” Mainline Tie Strip with ME Code 70 weathered rail - gorgeous other than the ghastly anchors every five ties. 
   

Left (ME Code 70) Right (PECO Code 83)

CVT rail anchors

  The prototype sometimes uses something similar that they knock on from the outside of the rail, so you might just need to cut off the inside gauge part. I remember watching the section gang hammer them on. Seems like they might have been calling them sleepers and they had something to do with keeping the rail from creeping, but that was over 60 years ago :> ) .....DaveB

Time and effort

I mix brands of turnouts and track for different reasons. Sometimes it's out of economic necessity like when I had a bunch of Peco code 75 turnouts from an aborted layout and couldn't afford to buy anything new. Other times it's because I feel like a certain brand is more convenient for the purpose at hand. I will use Atlas code 83 remote turnouts wherever possible on hidden trackage because they are just dead simple to use. Why go to all the trouble of installing an under table switch machine when no one sees the turnout in normal viewing? Otherwise, I use Peco code 83 in all visible areas because they are well made and I manually switch the spring loaded points with my hand. I could go to all the trouble to drill holes and then bend and adjust home made over center springs on matching Atlas turnouts but by that time I might as well have just taken the time to make the rail joints between the Peco code 83 and the Atlas code 83 Flex. Besides, it's just not that big a deal. It takes me all of ten seconds tops with a soldering iron and a fine set of needle nose pliers to make a joint between the two different types of rail. I might have to do a tad bit of filing but more often than not, I don't even have to do that.

As far as appearance, that's just personal preference. My old eyes can't really tell the difference in the various brands of track once it's ballasted and painted.

For me, if ME code 83 goes

For me, if ME code 83 goes away, it appears the Peco 83 is next closest thing. I have 6 bundles of ME code 83 non-weathered track ordered that I will pick up from a vendor at the Oklahoma City Train show on Dec. 15. According to my calcs, these 6 bundles should see me through to end of my layout construction as it now stands. In anticipation of my layout build, I have been buying one, two or three bundles of ME track at different shows and hobby shops over the last four or five years. I have also seen the bundle price go from $26 to now $33.

I also used Atlas code 100 in my helix and staging yards along with Peco code 100 turnouts. They work well together.

This may help with Code 83/70 Transition

From an RMC summary of a Peco press release

"As many modelers typically combine Code 83 and Code 70 track on the same layout, PECO is also introducing the availability of their all-new SL-115 PECO Streamline Transition Track, which incorporates sections of each type of rail to enable a smooth transition from one to the other. Each SL-115 package contains four transition tracks."

see https://rrmodelcraftsman.com/peco-expands-ho-code-70-track-line/ for illustration. 

There is also an SL-113 transition pack for code 100-Code 75 (UK Finescale track) transition. 

  "According to my calcs,

Be generous on your estimate. I thought i was allowing enough extra for trimming waste, etc. but came up about 5 flextrack sections  short .....DaveB