The 5S was a great phone, but it's three years old already. I wouldn't recommend getting a 5S now that the SE is available, unless you're getting a REALLY good deal on a used one.
The SE is the exact same form factor as the 5S, but is substantially more powerful, has longer battery life, a better camera, twice the RAM, etc, etc. A SE is going to have a lot longer usable life for you in the long run, as it has plenty of power for the apps and OS updates that are coming in the future.