I've grown particularly fond of my David Boye folder with the Blue handles. I always liked my yellow one but never carried it much. The blue handles go well with jeans but the knife is so care free. I can wash it out anywhere , a faucet, stream, puddle, or pond it doesn't matter, and with little care for what water or moisture will do to anything because it won't hurt it at all.
It holds an edge just fine in my opinion and hardly needs any maintainance at all. So I love that one a lot.
As for collector pieces. I like my two Scagel reproductions from Northwoods and I like my old classic original Sportsman folding knives by Gerber a lot. I am also quite fond of my Mike England folder which may be the only one he ever made before he passed away. These are great knives that I love for the fact that I have them and few if any other people do.