Re:
I'd second the AMP B4 and B5. Never ridden the B3 or its variants.
They are light, fast, climb well, and still look so sharp. Just don't expect DH travel. They are XC racing bikes that evolved into the Specialized ranges of the later 90s.
I do have 2 URT bikes, Ibis Szazbo and Klein Mantra. The 'sweet spot' Szazbo is the better of the two, with around 5" of body the tunable rear travel and no too much variation in the crank to saddle length, but they are both very weird to ride. Best avoided for serious riding.
All the best,