1) PM2. (The original Paramilitary was a nearly knife, and the PM2 nailed it.)
2) C95 Manix. (Maybe if they produce a CruCarta Manix 2 XL, that will displace it, but there's just something about the thunk of the original Manix's backlock that wins me over.)
3) This one is really difficult to narrow down to 1 knife. It's basically all those weird and wacky Spyderco designs that you're not interested in until you handle one and suddenly appreciate the genius. E.g. Hundred Pacer, Tusk, Smock, original Dyad, Lil Temperance, SuperLeaf.