I've ridden both, risers and a wider board. I also liked both at the separate times they were used. As far as performance changes, the risers "stiffened" up the board, and also seemed to increased leverage with leg moves. I tried them on my freestyle board also as a joke, and found out they suck in freestyle situations (have to reach farther for grabs, etc.). Downside to the risers was extra weight (which in some cases was a plus, but mostly a minus).
I didn't notice a drop in performance from the wide board I rode this year. Everyone says it's slower edge to edge, etc., but I did not feel a difference. The board did not feel sluggish and was actually nimble in moguls. The stability in park riding (rails, takeoffs, landings, etc.) was a huge plus, not to mention lots of fun in powder. The overall flex was softer than I prefer, but that's what you get with a jib board.
This year I'd like to get the same width board in a much stiffer version for freeride use.
I think the best advice for someone is to actually ride both and decide which they like better. I know a few freaks who have to use a wide board and lifters. They want to carve at high edge angles without drag though. It all depends on what performance you want out of your ride.