After the WHMCS hack and vulnerability debacle a few years back, I tried Blesta. Would have been a perfect time for them, but their importer just kept hanging and hanging. When you can't get something as simple as an importer right, it means it's time to just walk away.
Tried CE, same thing. Couldn't even get their importer to fire up, too many problems.
Needless to stay , I stuck with WHMCS. While their support is painstakingly slow, they do show remarkable improvement in the development cycle, even if it does mean increasing owned license costs every few years