Bids for freshma

depends on who you are
if you get to know 3+ guys on a decent level in a normal fall situation, you're probably fine.
be at their events, be yourself, and be connected, and you should be good.
in a normal semester it's the guys who don't make any friends in the houses beforehand who get hosed.
pick one as your favorite but be open and present at the other just in case.
delt and snu always have more guys show up in january than they take, so you have to have an in before january to keep yourself safe.
you could always like take one and check out another mid too, as a safety and good perspective. a lot of guys find that they just need to meet a few guys in each chapter to see what the good fit is, and then its comparing fits rather than comparing frats

Sig chi is easy, just show up to the minimum amount and last I checked Snu is Bottom tier. Not competitive at all anymore.

100% Depends on the frat. The ones you listed will all be decently competitive besides Delt. Delt gets desperate to get a decently full pledge class (and never does) and end up giving out bids to anyone who is interested in the chapter, that's why all the creepy boys are Delts, they all got rejected by SNU. If you are a freshman, it will become extremely obvious during rush week when the whole house is on display.