PvP: Swampert. Sceptile already has LB while Blaziken doesn't bring anything to the table even with BB that would compensate for its glassiness.
Raids: Depends on the raid bosses. There are no legendaries in gen 4 against which any of them are relevant, but in gen 5 we get Swords of Justice, each of which has a weakness to at least one starter type. Unfortunately for the starters, there are a fair number of better attackers against most of them, but against Cobalion, C/BB Blaziken seems to have the highest DPS of any pokemon.
They'll all become the top non-legendaries of their types and there are always reruns and non-legendary raids to use them in, if they get the starter exclusive moves.
Focus on the ones that are most time sensitive. Treecko first, then Torchic, then Mudkip.
