Well, to be quite honest, it does not matter how you want to portray your own character. Whatever makes you feel comfortable with portraying yourself is the key - if you don't like adding a double chin or extrarolls of bodymaterial, maybe just draw your character a tad wider than the regular size?
However, I see no bad idea in portraying the characters in different bodytypes. Actually, I think it might bring them more depth, considering some are really short, others are tall, skinny, heavy, fit, etc.
Well, go with what you think is best. After all, it is your comic! Also I was thinking the other day, when you start doing size differences it might start being weird to have everyone the same height, and then it just gets overcomplicated. Having all the characters about the same size probably helps with the synergy.
I'm pretty much indifferent to the change to be completely honest... It's a good idea - mainly you get to portray characters in a wider range of styles now (pun is completely unintentional, I swear!). But to me it's a cartoon/comic - I really couldn't care less if someone was skinny or fat or whatnot... as long as I get to identify and recognize them, I don't mind