Well, first off, for the scripts, it all depends what client you use, and what you want to write. As for the best client to use, it is all up to personal taste, as well as what is out for your Operating System, some good ones

X-Chat (My personal favorite) (Windows and Linux.)
IRSSI (My favorite CLI IRC client) (Mainly Linux, though usable in Windows with cygwin.)
MIRC (Alot of people on IRC.UnError.com use mIRC. (Windows, though usable in Linux with WinE)
KvIRC (Linux)

There are tons of IRC clients, you just need to find one that is right for you.