Well...the training camp gets you the Cerberus, a really good light melee unit with a long movement range. It is much more effective against enemy mages. A lvl 5 armory will let you train 8 more units at a time (it's giving you 6 now; it will give 14 at lvl 5). If it were me, I'd do the training camp, and immediately start stocking up to do the armory asap afterward.
Edit: didn't see Aramina's post, but I agree!