I can't give you any advice on anything other than PHPFox, Handshakes and Buddyzone, e-friends (alstrasoft) and Boonex Dolphin ... although I've used a few others - but I can say "keep searching" and you'll find plenty of reasons to use and not to use certain scripts...
I know if you put "PHPFox" in google - the first listing is a thread that's bashing PHPFox - but that was made by a guy who never purchased PHPFox and there's even a guy on there bashing ME because I had him banned from the forums for stealing other peoples work and selling it off as his own. Yet he claims I was stealing money from other people...
It's always interesting what you'll find if you just search. You probably know what you need for your idea - so check out the demo of PHPFox:
http://www.phpfoxdemo.com and see if it's what you need or not... check the forums:
Read their testimonials on the front page as well. There's a TON of sites with over 50,000 members on them and they're all running fine... yet you may hear people complain about speed and efficiency. Everybody has their own problems... it just seems PHPFox gets a bad wrap from competitors who try bringing them down.
So read around and take some threads with a grain of salt. PHPFox owners on Sitepoint and Digitalpoint are always finding those threads attempting to bash the script they use and they'll give you the truth. The people who start them usually have 1 post or the others who "come in to help" have 1 post... you'll see the pattern
DZOIC (handshakes) would be the second best in my opinion but again, try out the demo. I don't know if they have a Lease option yet but PHPFox and BuddyZone does for sure.
I honestly can't say much about BuddyZone as it would make me sound biased but believe me - spend your money with caution and never tell the truth about their script even if it's 110% true. They'll call you a liar on public forums and claim you stole their script... you can imagine how their customer support is they're a shady bunch, period, and there's a few others on here that would definintely agree with me (ex-customers).
Dolphin is an okay script and I believe they're getting better but read their license carefully as it may or may not be for you... some are fine with it and some are not. It's a nice little script though.
Zoints looks cool but I believe you're looking for a stand alone script and I'm not experienced with it - I just know you need vBulletin for it and not sure if you're a license owner or not?
... you might even check out Mugg Shot from Red Hat? Looks promising but the license requires you to host it on your own server.
Anyways - do your research before buying and read what real script owners have to say...
Whatever you do - stay away from Alstrasoft... unless you love lots of problems and fixing lots of code :rofl: