This is actually a surprisingly difficult question for me. Partially because I genuinely don't know what I'd say, and partially because I've had very little concert experience so haven't got much of a benchmark to go off. On the one hand, if I like this artist/band/whatever, I'd presumably think that they were good musicians; however, I wouldnt want to just listen to them playing all of the songs off their album in the same way. I want something special from the concert, given that I'd probably be paying a fair amount of money accordingly. On the flipside, a sub-par musician with an above-par pyrotechnic budget would certainly get my money's worth from entertainment, but I don't know if I'd feel anything apart from bombardment and sheer dazzlement (wait, is that even a word?)
I'm probably going to go with the better musicality. Watching stuff like The X Factor has highlighted to me how you really can't polish a turd, even if you flood it in lights and back-up dancers. The contestants on shows of that ilk are very much sub-par singers - especially in a live context - drowned out by the background. Provided the venue was suitably intimate, and the ticket prices cheap, I'd much rather go with the sparse awesome musician.