Hmm...difficult to choose, I'm using all 3 though for the frontiers. If you haven't beat the game, I'd prefer Blaziken. Swampert is fine, you can add Ice Beam. Sceptile also, his Leaf Blade get STABed if I'm not wrong. Well, here are my 3 starters movesets:
~Blaziken: Slash, Rock Slide(breed), Sky Uppercut, Bulk Up
~Sceptile: Leaf Blade, Crunch(breed),Dragon Claw (TM...),Thunderpunch (move tutor at Battle Frontier)
~Swampert: Surf, Ice Beam (TM), Earthquake, Rest(TM)
--Btw, yeah, only Blaziken can deal super effective damages on Norman's, but consider that Norman's team Sp.Def are low, using Sceptile or Swampert is also good