I am a long time Java developer on JBoss(and Tomcat). In the last year I had to develop over WebLogic and I have to say - I really miss JBoss.
Since my experience with WebLogic is pretty shallow, I am asking the more experienced guys out there: Is there a reason for spending money on WebLogic? Isn't JBoss giving you all that you need?
I suspect the reason Weblogic gets chosen is a pleasant sales person comes to visit a manager with money to spend, gives him the sales pitch and hey-presto, the company is using Weblogic. I don't know if the JBoss support contract comes with a sales force, but would be surprised if it did and that the playing field has leveled in that respect.
In my experience, other than the pretty console you get with Weblogic (which isn't worth forking out the license fees for) there's not much between the 2. I suspect these days JBoss has market share (just guessing that), which in my book that translates into more help available online, etc when you're stuck on something.
It's also worth considering that the Weblogic licenses (last time I saw them) where the usual server-side terms - per-processor, per-box, etc. This will limit you in scalability terms because with JBoss you can keep adding hardware without occurring extra cost, while with Weblogic your licenses will need upgrading too.
Whichever you choose you're going to be able to build your system on top of them without too much trouble, but my preference would be JBoss.