Shop around for an axle, maybe look for used off a bike being parted out. But to answer your question I would go with the spacers on the rear simply because they tend to be less expensive...the standard length aluminum hubs I ran from LSR only lasted about 25 hrs before the splines wore out.
I have a set of front spacers for sale if you want to go that route. I'm with everyone else on the subject though, they're good just to ride on. I'd leave em in the box when it came time to jump though