Hey, whatever works for you--stock is much much cheaper too. But for my old butt, and my wife's, the Fisher seat is an absolute godsend.
And surprisingly, so far I have not noticed the wider portion of the seat to bother or affect my stand-up riding at all! Go figure. They said that their wider rear seat would most likely not be much of a bother at all (they were right)--and certainly the softer, better foam is worth any possible future issues. And heck, if I'm inclined to race it or something, it's just 2 screws and 2 minutes to fit the stock 2X4 back on there.