i agree with DoH and Mathos mostly... except i have to argue the usefulness of the peach/shiek team... for some reason, at MOST of the tournaments i've been too, there's almost ALWAYS a peach/shiek team that ***** everybody in their path until they get to well known or highly skilled teams... for instance, back in az we have dark and light, they always rank very highly in teams matches as peach/shiek. in NM there's allboutpeach and allboutshiek, same thing. i'm pretty sure i've seen drew and DoH before as that team as well, and recently my friend chris and i won a monthly with it.
in my opinion, shiek isn't a damager. hence why i agree with mathos that she needs someone to rack up damage like ganon or marth or falco. peach is fairly universal, as her downsmash can fulfill both of these needs, she almost never dies, and under the right circumstances can float off screen and hit you back towards the stage. mostly you have your partner rack up damage, while keeping their partner away, then you switch off and finish them off with a slap while your partner is comboing/racking up damage on the other one, then you just keep that going.