currently heres how I see FF on a scale where 1 is the most:

Linear:
1. X 2. XIII 3. IX 4. VIII 5. IV 6. all the other ones I've played, possibly not including V are pretty much do what you want, especially X-2 and XII
Gameplay quality in battle
1. XII 1.5. XIII 2. X 3. all the other ones except 1+2 4. 2+1

Sidequests: 6,12,10,10-2,7, and 9 have a bunch of sidequests, 5 has like 2, 8 has a few really long ones, 4 has maybe 2, 1 and 2 have none.

Really all good games, but....