I believe the OP's question was, what is the best solid state amp YOU have heard? not what is the best solid state amp out there.
As some have mentioned previously, it is definitely system dependent. However, if you listen to a particular system and simply swap out the amp with another one, not changing any other component, match levels and listen, then, you definitely are listening to particular amps. There is a poster here on Audiogon that was initially demo'ing amps. I believe he has well over 13,000 posts here now. However, the problem with that is that no way did he listen to the amps in exactly the same system. He changed out many other things along the way. So, no way can you tell me that a person can offer 100% solid opinions on a particular piece when the system you heard other amps in was different.
other than that, I like his forum.
I have demo'd many amps in stereo stores. Stereo Design in San Diego (owner now retired), liked me over the years such that If I wanted them to swap out amps/preamps, etc. to A/B them, they did it. They knew that if I really liked something, I probably (eventually) would buy.
Top of the line Stupidly expensive Boulder amp vs Audio Research REF 250 or REF 750. Believe it or not, the Audio Research amps beat out the Boulder.
Mark Levinson 23.5 to me is still one of the best amps I've heard A/B'd with other amps in the same system. Remember, you must match levels and then listen.
Mark Levinson ML-2, Bedini 25/25, Nelson Pass 25W amp. with efficient speakers, wow!!!!!
And yes, I have heard them in the same system, comparing them to other amps only.
This is just a few, there several out there. the problem is People are trying to remember what something sounded like in their or another system and then later on changed out the component (or many others) often without direct comparisons and matching levels and going by memory.
Many of the amps mentioned are actually pretty darn good.
I know this is a system and not just an amp, but the only system that I've heard that actually disappeared was at Optimal Enchantment in Santa Monica, CA. Stupidly expensive Basis (top of the line) turn table, Audio Research REF10 phono stage, Audio Research REF10 pre-amp, Vandersteen 7A speakers and yes, Audio Research REF 250SE amps. Cables were top of the line (thick as a snake) Audioquest cables. never heard a better system or one that disappeared like that one. Wow!
enjoy