ML IBD or MS FICC?

Agree with Jimbo that it depends what you're interested in. That being said, having friends who did s&t internships, it didn't sound like they did all that much during the internship (since you don't get licensed during the internship). I know banking hours are bad, but sitting at a desk from 7am to 7pm doing data entry and getting people coffee sounds worse to me. It seems like you'll get much better hands on experience at a banking internship, although I did a banking internship so I can't comment personally on s&t internships.

If you’re not dead set on doing s&t, I’d go for banking. The people I know who did s&t internships and loved them (and went back to s&t) all were dead set on trading..they weren’t even interviewing for banking positions.

Don't turn this into a MS vs ML decision since the functions are totally different (s&t versus ibd). Don't take MS thinking you can just switch into banking after the internship...I've heard this is extremely difficult at most firms. Firms make switching divisions after the internship extremely difficult (if not impossible) since they don't want people accepting internships in divisions that don't interest them with the purpose of switching divisions after the internship. The purpose of these summer analyst programs is to test out people for next years full-time class, so they don't want to set the precedent that they're willing to waste the slots in a given division's intern program on interns who want to switch divisions ultimately.

Also, just a side note..MS isn't a top fixed income firm anyway...the top players in the fixed income space are Goldman, Lehman, and Deutsche. You can't apply the same rankings from the M&A space to the trading space.

I'd take the banking internship. It will give you far better experience, and you won't have much trouble trading up to GS/MS/top boutiques after your internship (if you want to) if you get an offer to return.