I have 5 Spyderco knives, and I love all of them. The only one(s) that I wouldn't change would be the Dragonfly 2.
Chaparral: Full CF, no-liner handles. I know it's the way it is for cost, but I can dream.
Delica: It's as good as it'll get, for the most part, but it's an outdated design. I wouldn't change it, per se, but I don't think it's "perfect".
Techno: It's pretty close, but I would probably change the backspacer to standoffs. I also might trim the blade thickness down a little bit, but keep it pretty stout.
I'm getting a Mantra next week, and it looks to be as close to perfect as I want out of a Spyderco. There's nothing I'd change on it, so far. I'll have to use it for a bit to be sure.
Current: Dragonfly 2 ZDP-189, Chaparral 1, Techno 1, Delica 4 HAP-40, Dragonfly 2 HAP-40, Mantra 1, Ladybug Salt Hawkbill, Nirvana CPM, Endura 4 HAP-40, Sage 4, Para Military 2 CPM Cru-Wear, Sage 5, Caly3 HAP40, Sliverax, Lil' Nilakka, Chaparral Raffir Noble, Zulu, Manbug HAP40, Meerkat HAP40, Sage 1/Sage 2/Sage 3 CF, Introvert, Techno 2