Zerocash has a GCHQ/Israel/NSA backdoor.
Anoncoin devs consist of one fat neckbeard trying to do all the work (or claiming too, the commits I've seen consist of "changed namespace name")
Darkcoin is rumored to have a 5% pre-mine
http://www.devtome.com/doku.php?id=a_massive_investigation_of_instamines_and_fastmines_for_the_top_alt_coins#darkcoinBytecoin has bad software
that is undocumented with no GUI wallet, and the devs aren't transparent enough to say "we're working on it goys!"
Bitmonero is a shitty clonecoin made by a brazilian/paki/indian who claimed to be Ukrainian, just a source copy of Bytecoin with no real dev team or plans to actually make the software more usable.
Bytecoin also has an 80% premine.
Bitmonero probably won't have a GUI wallet until the Bytecoin devs make them one.
I'm not too interested in Zerocash at the moment, the developers would really have to go out of their way to practically livestream them starting the network and "forgetting" the master key.
Darksend will hopefully be finalized soon and on the way to decent ring sig software.
Bytecoin devs could improve too, Bitmonero devs (what devs?) could put forth more effort than changing a few variables and releasing a clone-coin, Anoncoin could implement the same Zerocash as the Israeli researchers and "destroy" the master key... Darkcoin devs could address the "premine" allegations again.
Still a gamble.
Edit: it is documented, and there is a 3rd party GUI wallet now