In my limited and a-few-months-old experience I would say if you want to do EJB3 then use GF instead of JBoss 5 (*). If you want to do EJB2 then it's a toss up. I have found the GF public support forum (i.e. this one) more responsive/helpful than JBoss's but YMMV.
(*) I've been doing relatively unusual stuff involving JCA and XA so I can't really attest to "normal" use cases.
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