Good question. Got screwed in the past with bid/ask spread compared to SSO/SDS. I need to start watching both again to get feel. SPXU was the one i got messed up on. Now SPXS exists.
main thing is when I trade SDS/SSO I am trading 1.5 posistion. lets say one posistion TNA/TZA = $100 then I trade $150 SDS/SSO to get same dollar return per % move. I rarely get 300% leverage so margin usually doesnt come in to play much.