Shulk because he has the power AND the attitude: He's all about a well deserved revenge in the begginning. What's not to love about phrases such as "Talk all you want, cause those words will be your last!"?

I'd put Melia second because she has awesome magic and has to go through much more than the others.

Fiora is third because of her awesome fighting style and hot as hell design.

Melia. Spear Break + Starlight Kick is so OP.

What's wrong with Sharla?

I'd take her over Reyn or Melia personally.

I just think the other characters are better.

Fair enough, the way you worded it just made it sound like you had a particular problem with Sharla, that's all. :p

Heretic! Heretic! Who likes sharla over melia or Reyn?

Zanza and Dickson.

This is a game where I actually prefer the bad guys over the good guys.

Dunban, because he's very likeable.
Also, for some reason I tend to really like the first character we see in a game. In most games, that would be the main character, but in Xenoblade's case, it was Dunban (and his buddies ).

Hero-pon Riki, because I like cute things, followed by Reyn just because he's such a goofy jackass.