For me the key drawback about Mendeley is a very limited ability to control the citation keys. Even on Zotero this is a second-class citizen, since you have to install a plugin.
Have you been able to control the citation keys on Mendeley? It's been a while since I've tried it now...
Sorry, slow response. Every item has a Citation Key field on it in the details. Just put whatever you want in there. Annoyingly it doesn't show up until after you try and export or copy it the first time. I just hit Ctrl-K to copy the citation and then change it if needed.
Am really curious about JabRef though that other people are mentioning. Haven't used it before.