I was discussing this with a friend today:

I've only played through FF1, 4, and 6 completely. I've played 5 a bit and tried X, but 3 hours in I just couldn't stand it anymore. We determined over the course of the conversation that I enjoy mostly fast-paced, non-linear games. To that end, he recommended FF 7 and 8 for me, but told me that I probably wouldn't like X at all, as he described it as "a straight line." What do you guys think? Which FFs do you consider more linear than the others, and why?