I'd have to say the 0550/1 or 0560/1 are my two favorites. They're just solid and great all around knives.
I've owned several ZT's and those two come out on top.
However I did EDC a ZT 0301 for quite a while and loved it dearly, it is a great knife. I never really found it too big, just wish you could de-assist it like you can the 350. I love the manual flipping action on bigger knives for some reason, so the 0200 was amazing and my ZT 0560 is a close companion to me.
But I also just love a manual folder so the 0550/1 worked as well.
It all depends on your preference.
Do you like large beefy knives? If yes, you can't go wrong with the ZT 0200, 0300, 0550, or 0560.
Would you prefer a large beefy knife with manual action? If yes, ZT 0200, 0550, 0560.
Would you prefer a large beefy knife with Assisted opening? If yes, 0300.
Would you like a thinner less space consuming ZT? If yes, get an 0350 or you can still pick up the 0400.
ZT's I've owned:
ZT 0200
ZT 0301
ZT 0350
ZT 0400
ZT 0551
ZT 0560
Any one you go with will be an excellent choice.