I only have one of their ex-BB RTR cars, a CSX Caboose. Nice paintwork, pity the wheels weren’t in gauge (and they were one-piece wheelsets so you can’t solve this other than by replacing them). I also have a couple of their Bombardier bilevel cars which are superb - nicely heavy, good detail, all you need to do is fit Kadee #58s in place of the plastic couplers they’re delivered with and they run very well indeed. One tip I found was to add a drop of light oil to the inside bearings as this really improves their rolling abilities.
I’ve got a fair number of Athearn RTR Locos and not one of them has given me a problem. Their newer RTR rolling stock is very nice. They come with metal wheels now, very crisp paint detail and you can’t beat the price. I’ve got around 30 now.
I have some older Athearn locos. Like the F7 for which I love. Some Fy I have had for more then 20years and still running just great. When I first got started in model trains, I wanted a fleet of GG1s my favorite loco. I ended up with a fleet of Athearn F7s. For the prices, you can’t beat them.