the only 2 client that i used in 2012 client ..xD
currently using 2012-06-18 in my test server ....
for stability you are recommend to use 2012-04-18 since it's recommended client and supported by rathena officially.
Yep, 2012-04-18 is a great client and is very stable.
2013 clients, you could try 2013-07-31, 2013-08-07, 2013-08-14 or the latest client from kRO (2013-12-23).