I was on T-Mobile no-contract/no-subsidy plan for three years. In that time I purchased the following phones used:
Samsung Behold II - An embarrassment, sold it back.
MyTouch 3G - I loved this phone. It was tough as nails and I wish trackballs o phones were still a thing
MyTouch 4G - I got screwed on this used phone purchase, I think. It had water damage. First the screen digitizer went. I replaced that and then dropped it like one foot on the carpet and lost screen entirely - just black.
Samsung Galaxy S - I really liked this phone and other people must too, because I bought it for $150 and sold it for $130 a year later
NOW, I am on Verizon with a Galaxy Note II. My phone has some sort of short circuit, which I hope isn't a thing with all of them as I am getting a replacement under warranty soon. I decided I wanted the newest latest thing and my wife's workplace is only served by Verizon, so there it is.