Alright, I was in the same situation as you and my choice was pretty easy. Maybe eeter1 can chime in as well as we had a whole discussion on this in the USC thread...
I think it really depends on your personal preference on weather (LA vs Pitt), girls (I dont think thats even a contest), which country you are considering working in (USC has a huge presence in ASIA and LA, but nobody else really gives a damn about Marshall), School culture (Marshall- commuter school, not much networking, rich kids driving lambos & Aston Martins vs. Tepper- small class size, quant focused, group oriented, more tight-knit feel), industry ( Marshall- Entertainment vs Tepper- IB + MC), strength of alumni network (Marshall holds a huge advantage here) along with many other factors such as city life, family, blah....
But looking at it holistically I chose Tepper as it has a better reputation than Marshall, the quant focus will get you in some doors, and just knowing the caliber of student at Marshall (a lot of my friends go there, or went there... Im really not impressed).
Hope this helps.