Here's mine:
From easiest to hardest:

1. Yuna: Moon Sigil: Easy if your Yuna's stat is good. Requires Anima and Magus Sisters, PAL player becareful! Strategy is needed if you're too weak.
2. Auron: Mars Sigil: Totally easy when you're doing Monster Arena sidequest. But some are frustrating.
3. Rikku: Mercury Sigil: Three things needed: 1. Patience to walk again and again. 2. FAQ to make things easier. 3. No Encounter to support your life from boringness.
4. Wakka: Jupiter Sigil: Definitely hard if you think Blitzball sucks and totally hard if you're never get too good in it. I never have problem in this except the BORINGNESS of playing all of this for like 4 hours!
5. Lulu: Venus Sigil: Reflexes are important in this part. IF your reflexes is good, try three-bolts area, IF your reflexes is bad, try one-bolt area. Once again, patience!
6. Tidus: Sun Sigil: Depends on luck. IF you can grab all of the balloon in the first course of the race, that's fine but the second and the third part are nasty, birds attack! And balance is important!
7. Kimahri: Saturn Sigil: Even if you know the track, you still need speed, Tidus's running is crapper than Yuna in X-2. And mistakes aren't avoidable....sometimes.