Can't go wrong with any, but there's a bit of variation there. The Millie being quite a bit larger than the rest.
Which Native were you looking at? The s30v Native was my first Spyderco, and I truly love the ergonomics of this knife. It carries very thin and light in the pocket, but fits in your hand like a larger knife because of the choil.
The Endura is a staple in the Spyderco line up, great EDC.
Shouldn't be anything "wrong" with the tip or lock on a Military. The tip is rather thin, so I wouldn't try to stab through concrete with it, but it's not glass either.
The stretch LOOKS like a perfect EDC for me, but I've never handled one. Seems like it has everything going for it, though.
If you have somewhere to fondle all of these, that would probably help. Several of these models are THE knife for certain people, it's just hard to say which one until you've handled them all. The Endura and Millie seem to have the largest following out of all of them.