Don't know about the other two but vTiger is the crappiest, buggiest piece of shit I ever had the misfortune of handling. It's full of legacy crap from a bygone era when the original developers wrote it first in procedural PHP. Then the subsequent version in a horrible mix of OOP.

The software API's are horrendous and extremely hard to work with. The entire architecture is screwed up and very hard to grok at. IMHO it is best to keep away from this project.