From reading your bio, I would advocate U of C (Am attending so take the bias as you will). In terms of general academic firepower and prestige of faculty, this school is easily top 5 in the nation. There’s plenty of fluidity in terms of social life, if you want to go out to frat parties there’s usually something going on every weekend, and if you want to stay in having deep intellectual conversations there’s plenty of people doing that too. People on CC love to maintain this “fun goes to die” stereotype, but honestly it’s not that academically rigorous so long as you manage time effectively. Econ major is somewhat difficult but not excessively so. In terms of Urban focus, you’re in one of the biggest cities in America, so obviously the number of available internships and research opportunities is immense. Our career services department is pretty excellent, and so long as you don’t completely slack off it wont be hard to get summer internships and jobs.
With regards to Pomona and Amherst, I would honestly find the small class size a huge limitation in terms of social life and future prospects. Half the college experience is meeting highly motivated successful peers and thus enriching yourself through knowing them. Within houses and greek life, there’s no shortage of community at UC, and your classmates are incredibly smart connected people. Small schools, especially athlete heavy ones like Amherst, would probably have a much more rigid, stifling social scene than U of C, which is very open and inclusive.
Personally, I’m very happy at UC and I would choose it over either of those schools without hesitation.