Probably the Se-users (ENXJ) have a little more natural drive for sports. Si is a more observant force in interacting with the world, where Se is actively looking to interact.
With these types, those are the only natural inclinations, while I think for non-Se-doms (or Se-aux) those are very strong, for other types cultural factors and upbringing are more likely to be the reason for someone to spend a lot of energy on sports (and excel because of that).
So I think these might be a toss-up honestly. If you'd put a gun to my head I'd say ENXJ, but I have nothing but gut feeling to back me up there.
Type has nothing to do with physical ability or awareness. Strong sensory experiences make a greater impression on the high Se user, while the Si user is impacted by things that are less directly sensory and more difficult to predict, but this doesn't translate into one being better at sports at all. As @spaceynyc said though, it is possible that Si users would be more likely to enjoy repetitive sports than Se users, Si seems more suited to handling repetition, as that is a cognitive thing and not a purely behaviour-based trait.
Reality: Whoever is dedicated to fitness and physical technique of that sport. There are out of shape people of both types and others who are in shape but not actually fit whatsoever. It's impossible to make generic statements about either type's physical ability and have them hold up consistently in reality.
In parallel universe of typology: ESxJ assuming their type translates to socionics as-is. In socionics, ESxj have 3D (3 dimensional) creative Si and 4D demonstrative Se whereas ENxj have 2D Se and 1D Si (their vulnerable spot). Meaning ESxj have much more capable sensory functions. They can understand it in ways that ENxj can't. So if you compare ESxj and ENxj who are:
- equally capable at the beginning
- equally interested
- able to dedicate an equal amount of time to learning a sport without any additional time to do research, get extra coaching or anything
Then the ESxj will learn much faster and be able to process sensory techniques (using both Si and Se) in ways that the ENxj can't because of access to those extra dimensions for their sensing functions.