I still have a while to go with my Tyranids so far, mostly painting, but I'd figure that I will probably want to collect a second army someday. I was thinking of a couple of different armies to choose from but thought I'd see what you guys thought too.
Space Marines - being the forefront of the entire game of warhammer 40k, it seems to make sense to collect these guys at some point, that being said almost everyone has a SM army and can get kind of boring. Good armor saves and all around play style are big benefits as well as being almost entirely plastic.
Guard - I'm thinking of mostly collecting these guys for their tanks. Gunline is also quite a big difference from the Tyranids now (long range fire?). Unfortunately they still have bad armor saves and numbers so I'm not sure how different they'll be and if they're worth the effort.
Daemonhunters - This was the other army I was thinking about collecting when I first started playing. The idea of so few against so many is appealing. They also seem totally different from tyranids (numbers, armor etc.). The biggest drawback is that they are all metal and such a change could be challenging.
Witch Hunters - As far as I know they are similar to space marines (same armor saves, guns and things) but with slight variations. Unfortunately I don't know what those variations are and why they are so much more unpopular than Marines are. Never played against them or even seem them.
Necrons - The only nonhuman army I'm thinking about collecting. Good armor saves, very good range and tank hunting abilities as far as I know. Unfortunately not a lot of tanks (just monolith) which is one of the things I'm missing as a Nid player.
Anyway, I haven't had a lot of experience in general with these armies. I've only played one game against grey knights, and one game against IG. Never played crons and witch hunters so any advice you guys have or opinions would be appreciated.