The comb mostly. Tail feathers won't matter for awhile since the tail feathers and the saddle feathers, the ones that curl down just in front of their tail feathers, grow out later.
Combs seem to be the most helpful early on.
But you never really know until they crow or lay an egg!
Don't worry. Time will tell. I have ten 5+ week olds and am really sure one is a roo. The comb is HUGE compared with his sister and his behavior is now unmistakable. I will have to rehome him due to my city ordinances. Just enjoy them right now. Time will tell.
Nellie is really to young...