It all depends on what you want to do with the 1Hz signal.
If you are simply using it to create your own RTC then the next question is how accurate does it have to be? In other words, what latency can you afford between the rising edge (if that it the one you should use) and the actual update of the second's unit digit. (Apple claim that all of the Apple Watch second-hands move at exactly the same time all around the world, but they go to a lot of trouble to synchronise then. Therefore the question for you is do you need to go to that level or is something that is +/- 0.5 or 0.1 or 0.001 second OK?)
Also questions such as the supply voltage, maximum current draw (and possibly the related question of battery life), chip size, mounting requirements (DIP, surface mount, ball or pin...), do you need a crystal or is an internal (normally RC-based) oscillator sufficient and lots more all come into the device selection.
The requirement for 1 UART, 5GPIOs and (presumably) an I/O for the 1Hz signal should not be hard to meet once you have an idea about the other criteria.
Susan