My vote is for Progressive Suspension fork springs and 15w synthetic fork oil. The difference this $150 mod makes in the 'Strom's handling is nothing short of jaw dropping.
More power is great but will do you little good if you don't have excellent control. Stiffen up the front end a bit with Progressive springs and thicker fork oil and you'll swear you're riding an oddly comfortable superbike that can barrel into corners and handle rough pavement without a hiccup, yet ride silky smooth on the highway with far less jarring and jolting on poor surfaces.
I'll take tremendously improved handling and control over a few extra horses, anyday. The added comfort on the highway is yummy frosting on the proverbial cake.
Then again, if you don't believe you'll ever hit the brakes hard and have little interest in carving into corners with confidence and composure, get the cans and the Power Commander.
My three cents...