Kona Cafe used to have fried onion straws(which were awesome!) on top of their beef terryaki dish, but they don't serve them with that anymore. I'm not sure if they serve them with anything else.
I've never had them at Beaches & Cream but the ones at the Hot Dog stand on the Boardwalk are really good too. They also have good ones at Flame Tree BBQ in AK.
I guess I'm in the minority, but I thought the onion rings at Sci-Fi were average, at best. I haven't had onion rings anywhere else at WDW, but I'll have to try Beaches and Cream next trip-it seems to get rave reviews on all its menu items!
Beaches and Cream gets my vote!!!!!! Advise. . .go early afternoon for a late lunch. Beaches and Cream gets VERY busy in the evening. It is a fun, great place.