I haven't seen Forbidden Broadway (although I would love to), but we did see Second City when we visited Chicago. I guess I would vote for Second City because 1) it's a fun show and 2) it's a Chicago institution.
I'm not aware of any discount codes for Second City, but the tickets are only $14 for the Monday night show (Best of Second City) and only $19 for the Tue-Thurs night mainstage shows.
If you decide on Second City, I'd advise getting there early to stand in line to get the best seating. (No reserved seats.)
BTW, we are 50 as well and thoroughly enjoyed SC.

If you are a fan of Broadway musicals, you will probably like "Forbidden Broadway", you need to know the plays in order to get the jokes. I thought it was enjoyable and discount tickets can almost also be found at HotTix which you can buy in person or sometimes online, usually the same day or on Friday for all of the weekend shows

www.hottix.org

Second City discounted tickets are very unusual to find at HotTix but they aren't that expensive so if you want to do that, call the box office and reserve now. I saw "Between Barack and a Hard Place" recently and it was funny, more edgy and of course political than Forbidden Broadway. We went 1/2 hour in advance and got seats in the very back of the theater but there was a large party there that night.

Well, Second City is a Chicago institution, and the current show, Between Barack and a Hard Place, is a really good one. If you decide to go there, the nearby Adobo Grill is great--don't miss the guacamole made at tableside!

Forbidden Broadway is also very entertaining--the cast is incredibly talented, the pace nonstop. There's a great place down the street called Boka that I'd recommend.

I think you'd enjoy either of these shows--only you can decide whether you want satiric comedy and a little music, or madcap music laced with comedy.