I've done 3 evaluations of WebLogic, JBoss, and WebSphere. WebLogic won every one of them, hands down. Having said that, my simplistic guidance is this: use JBoss if you are NOT worried about scaling past several thousand concurrent users. However, if you intend to scale beyond that, you're going to need something with proven horsepower and robustness - that's WebLogic.
Note: app server vendors generally sacrifice technical features for stability. In other words, robustness is in dynamic tension with technical features. If you want new features, you get more bugs along with it. It surprises me how many technicians don't get that. But, if you think about why you don't rush out and buy the first new Windows OS version when it comes out, you'll understand perfectly why this is so.
HTH