first flip is deffiantely easiest w2w. my first 2 inverts were a scarecrow which i learned by accident while trying to go big toeside and then learned a hs backroll. both w2w
I found the tantrum to be easiest. Landed first try ever. Mind you i had almost learned scarecrows and backrolls at that point so i had an idea about air control but still. Just try the flip you feel most comfortable doing.