For me, I prefer the Mantra 1. Why?
1) Flipper. Obvious. Alternatives: Southard, Positron, Domino, Dice, Rubicon, Mamba. However, the Mantra has better flipping action, to me, than most if not all of those. Of the ones I've handled, the Domino is good and the Positron is good, but I don't care for the others' action.
2) Full Ti construction. This alone excludes all of the above. I don't hate the Domino/Dice scales but they're not great. CF handles I could do, but other considerations lean against those(Positron/Rubicon/Mamba). Southard G-10 is just boring for me.
3) Functional SpyderHole. This is definitely a personal preference, but I like having the hole. First, more opening options is a plus for me; slow roll to open in front of the public is handy, plus yes, I am a knife fidgeter. Second, I like the Spyderco aesthetic with the hole, and it makes the knife look more like a Spyderco.
4) Overall design. In combination with the hole, I like the look of the Mantra 1 better. It looks more like a Spyderco, and it looks like an updated Delica or Caly3. The Rubicon and Mamba just aren't my style. The Domino is probably my next choice after the Mantra, but the Dice doesn't flip well for me(I think the action was transplanted from the Domino but not adjusted enough for the smaller blade).
Now if you handed me a Mantra 2, I wouldn't turn it down. I just personally find that the Mantra 1 ticks all my Spyderco flipper boxes. All the others are missing something. I almost pulled the trigger on the Positron in lieu of a Domino, but when the Mantra came out I didn't do that because I didn't have to compromise on good handles(Positron) vs Spyderhole(Domino).
I've excluded sprints and models not yet released. Even so, I think I'd still prefer the Mantra 1.
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