I had doubts about JBoss with AS 6, but AS 7 totally rocks and flies on my system! I use this for all clients that don't specifically ask for Tomcat.
The latest version of JBoss EAP 6.0.0 starts up in a second and has most bugs ironed out. The latest version of AS that predates it by a few weeks (7.1.1) starts up a tiny bit slower and has some bugs. Althoughly understandable, there is a split between the AS and EAP series, with the EAP series being more stable but although open source can only be downloaded on an evaluation license. Because its open source, everyone can build their own EAP from source, but it's something the casual developer might not be able to do or might not be aware of that this is even an option.
Otherwise JBoss AS is one of the best servers around. Generally you should avoid the early releases, but after a while it becomes really good.
The Eclipse based tooling (JBoss tools) has some issues, but it's generally really good (much better than the GlassFish Eclipse plug-in).