This is mostly personal preference, but also combined with how their characters react to the sizes, and staying in character with Dean at all times.
I personally love the protective older brother dynamic from the television show, no matter how many times Sam proves he’s a badass (Sam Fucking Winchester, ladies and gents, don’t mess), Dean always goes all out to help his little brother. It’s a hard dynamic to achieve when Dean’s the size of Sam’s finger, and it makes staying in character as Dean more difficult, though I’ve had some success with Cursed Dean. Having both brothers tiny is also a favorite of mine, so you’ll see more of that for sure.
We’ve bounced around ideas for tiny Dean and big Sam, but nothing in the immediate future.
Brothers Apart 