it depends on what you need out of the system. Many users will vote whmcs, personally I dont trust its security or past record in security.

We use both CE and whmcs on a daily basis - CE is the more reliable. It also allows multi currency which whmcs doesnt at the moment. It's support system is far superior to whmcs and includes many features that kayako etc have.

Ce is also cheaper - you can get a limited client license from licensepal / licensehut etc for about $6!

Best advise? try both and see what you prefer.