Scalping on a fixed-spread or dealing desk broker is suicide, go ECN only. 1 pip or even less. IB, MBT/EFX, some other broker with Currenex, HotspotFX, respectively
Here are the spreads at a random interval on HotSpotFXi, detect nearly all spreads are 0.5 pip or less (except NZDJPY, at 1 pip). HSFXi is institutional though, minimum $100k opening equilibrium. Finest bet for retail scalping is IB (IdealPro) or even MBT/EFX.