Locally here, at the Agway stores, Walla Walla wins hands down for success, flavor, popularity, and size. Candy didn't seem to grow as well, and if the spring is wetter than normal (like last year), they don't mature well.

Another farmer at the market grew Ailsa Craigs last year and they were beautiful. I've started some seed to try this year.
Ann

we like ailsa craig too, which is good because they get pretty big. they kept into january for us last year. we chopped up the rest and froze them. we're growing them again this year.

keith in calumet

never grew the 2 you mention. Ailsa Craig Exhibition is an AWESOME onion. sweet as can be, keeps to late january (!) and are 5-6" in size. can't go wrong with ace. plant 6" on center they need lots of room.

tom

Tom If you are getting six inch onions and planting six inches on center you are not giving them [lots of room ] YOPPER

I grew a kind of onion from seed last year called "Utah sweet". I planted the seeds in the greenhouse in January. They grew so slowly, they were only little tiny spaghetti size plants when I planted them in the garden. Those little scrawny things got to be bigger than softballs and they were SO sweet. I would definitely recommend them. I still have a few of them, they kept pretty well, too.

yopper, they need 6" vs 3 or 4 so 6" is lot's of room relative to 'regular' sized onions.