Banners, And Buttons.. Oh my

I was just wondering, as I'm one of those people who have those weird 215x217 banners, (Not even) does anyone know if the small buttons (Don't knwot he size... if someone wants to post it, please do. ), 100x100 or another size of button/banner is best, or more appealing over another, as I do want to (once I upload it) have my website halfway professional looking.