I've been using exclusively those tiny class D amps in my main system and in my bedroom system. In the main system, tri-amped, I use a TA2024 tripath chip based Trends TA10.1, heavily modded, with a good linear PSU, and it sounds absolutely marvelous.
When my friend purchased his vintage Audioreference 126Dc speakers, they sounded like crap with his existing Musical Fidelity amp... we tried one of my tiny class D (SMSL SA50, 70$) and it sounded MUCH better (poor synergy with the MF amp, probably, but still, we are talking a 3000$ amp vs a 70$ Chinese "gadget").
My budget is low, before switching to those little marvels I owned and tried many vintage / not so vintage class AB amps, some class A as well, but they were either disappointing OR unreliable.
I'm not saying those are the best amps in the world, far from it, but the right ones sound very good, give them clean power from a linear PSU and they will impress, tweak them a little (capacitors, volume pot...) they will shine. For me, when you add on practicality, foolproofness, and the fact that they use almost ZERO electricity, there's no way back.