I hear a lot of negative things about the security of the pidgin code base. However, I like it and with OTR + Tor it is quite nice. I notice that IRSSI with OTR and Tor is a more popular choice with the the l33t haxx0r and cypherpunk crowds, however I have never been a big fan of the more traditional IRC clients simply from a usability point of view. Pidgin has a much less steep learning curve than other IRC clients imo, although it has been several years since I tried anything else and Pidgin was the first program I used for IRC so if you are old school in regards to IRC you may have better luck with less noob friendly and probably more securely coded alternatives.