newsgroups and irc aren't software
More like: Newsleecher and mIRC, but who would use IRC when they have usenet?
Bittorrent requires a struggle to find new sites every time your main one gets shut down. There's no "searches" and not a large library. It is fast for true p2p though.
Ares is like a bastard nephew to eMule. Emule can be slow especially dependant on your sharing ratio. It does however have many great features such as comments, block lists, fake reporting system, search, etc. It also has a huge user base, and probably the best retention.
My recommendation is newsleecher through usenetserver.com and eMule. Use newsleecher to get most of what you want while building up an ul/dl ratio on eMule to get those on demand files you may have missed on nntp. IRC to me is just a time killer. There are nzb sites (similar to torrent trackers) for Newsleecher also making header sorting a thing of the past.