I485 part 1 where it says expires on... should i put the date of my f1 visa expiration or the date of my i94?

It would be a very reckless thing for any attorney to advise you to fill federal forms without ever having a chance to review the intended submissions for omissions, mistakes, flaws or improprieties. In fact, that could constitute malpractice. If you want to complete it right, retain a licensed counsel.

You should put the date on your last I-94.

I agree with my colleagues on the point that you should put I-94 expiry date. However, since you are on F-1 (student) visa, your I-94 will typically say D/S (Duration of Status) as the end date. If you are currently in School, state I-20 end date. If on an OPT, put the OPT expiry date.