I have owned a few pretty good SS amps (and one hybrid). I am not sure whether I will ever have a "keeper for life," since there are other amps I would like to try, but I consider the following amps (at least close to) keepers. My order of preference of those that I have owned is;
1. Clayton M300 monos (my current amps) - Class A purity and a window to the source, with excellent power and authority.
2. Lamm M1.1 - Rich, textured, and dimensional, with excellent mids, slightly fat bass and rolled off top end. I could live with the slight darkness, but not the absence of air at the top.
3. Cary 500MB - Great power, only moderate build quality, but nice sounding at all frequencies, especially mids, and leaning slightly toward the warm rich end of things.
4. McCormack DNA500 500wpc, a powerhouse with good sounding bass and mids, but IMO slight issues at the top end, a touch wispy or not exactly pure compared to others.
5. Clayton M200 monos - In my system these offer about 85-90 percent of the M300's. May be better with less power hungry speakers than my Aerials.
Amps that would probably work with my speakers and my budget, and that I would like to try and/or own (no order):
Lamm M1.2 Reference
Lamm M2.2
Lamm ML1.1
VAC Phi 200 monos or 300.1
CJ Premier 350
Cary CAD-211 AE
Pass XA160.5 or XA200.5
McCormack/SMc Audio DNA 225 Platinum Monoblocks
There are other amps that likely sound great, but I have included only those with enough power to work with my 90dB dynamic speakers (no set, etc.), and I prefer to stay with fairly well known American companies.