Yes. Run the same type and

Yes. Run the same type and size coupler head on the entire fleet. You can either go all scale size or convert to KD 5 and its whisker twin. Trying to force different size couplers together is only inviting frustration.

          Pete

Haven't had problems.

I use KD #5's and 148's, and a friend uses the scale 58's.  We've intermixed cars without issues.  They uncouple over the under-track magnets, and also uncouple when using a hand-held wand.  They stay coupled when running the trains.  They seem to re-couple without needing a manual push.  At least, that's been our experience.

Also, we've noted issues when intermixing brands of couplers.  They usually will couple together OK, but can be a bear to get uncoupled, by any method. 

 And we've noticed that the Kadee couplers are consistently proper performers.  Basically they seem to do what we want, when we want it.

When running on our modular club layout, the bigger non-scale couplers seem better due to the roughness of track at the joints between modules.  The taller coupler can handle more track mis-alignment.

Totally agree on the taller

Totally agree on the taller couplers, and my Kadees are my standard.  I think the scale couplers by Kadee (such as on my PS-1 boxcar) are great for the straight-and-level, but throw in a grade or some uneven track and there could be an issue.  In fact that boxcar helped me not too long ago, showing that my grade was way too steep when it de-coupled and I wondered why. (my new 2-6-0 slipping trying to get up it with a couple cars was the clincher).  That grade now lowered to better standards, that coupler works fine, but if you look at it going up you can see things are not as they should be.  May switch it out someday.  No, that grade wasn't obscenely steep, it just added a dramatic effect with super-elevation thrown in, which may have added to the deception of its steepness.

On my recently upgraded and weathered Mantua Monon gondola I used Bachmann couplers complete with their box/housing.  I did this because I have a few of them lying around from upgrades (perhaps too harsh on Bachmann....besidegrades maybe??) to Kadees.  Seems a waste to have perfectly good couplers that just don't quite perfectly work with Kadees. Well, thinking on that, the plastic whisker is what turned me off in the first place I guess.

fake whiskers

Sort of like a paste-on mustache - - - .  I've had some disappointments with couplers that have plastic parts.  That plastic spring seems to fail too quickly.  When I have cars packed to go to the club they'll roll to the end of their compartment and if the coupler happens to touch, the spring will take a "set", and not work right after that.  I've had a couple of the plastic whisker springs break off, making the coupler scrap.  Of course, those tiny Kadee springs can go off on an un-approved field trip too, but at least they're replaceable.

Ocasionally I find molding flash on the inside of the plastic couplers.  It can inhibit free vertical movement, and at times has caused derailments.

Basically, though, all the couplers we have these days are pretty good.  But I suspect most of us will put Kadees at the top of our list.

Oh, and my friend also likes using the Sergent couplers........ scale, no non-scale uncoupling wire.  But my hand is not steady enough to work them without risking damaging something!