Websphere may be configurated easily: you have a web console which helps you a lot in configurating datasources, virtual hosts, message queues and so on.
The difficult part is to tune it properly (at least, generally speaking).
I don't think WebLogic (or JBoss) are so much simpler to configurate and to tune, if you want to use them at their maximum powerness.
They're all very powerful application server. And power implies complexity.