Tianjin University is the older engineering school, strongest in chemical engineering, architecture and hydraulic engineering. Nankai is the liberal-arts and sciences counterpart, with mathematics, chemistry, economics and history as its recognised strengths. Both are national-level institutions and both are considerably easier to enter than their Beijing equivalents.
The geographic argument is obvious: 30 minutes to Beijing by high-speed rail, with living costs around half. Some students use Tianjin as a base and travel to Beijing for internships, interviews and academic events — workable, though the commute is only practical for occasional trips rather than daily ones.