Corpus Christi/Port Aransas or South Padre Island for 3.5 day vacation?

Two early twenties driving down from Houston, main concern would be that SPI is too far of a drive given we're leaving Friday afternoon and coming back the following Monday afternoon. We could do both, but maybe that'd be too rushed. We could alternatively split into 2 weekends and do SPI for the 3 day weekend and and Corpus for a regular Saturday/Sunday weekend.

We're not interested in drinking or touristy stuff (like the aquarium/USS Lexington), mainly interested in the beach. Thanks!