There isn't much difference between them.

I believe zero's are much better than the x1 in terms of problems with dirt... and since you don't have X1's on your other bikes, you don't have a cleat compatibility problem (going from memory, but you would never go with x1 instead of zero unless you had a compatibility problem).

Light action has a less-stiff spring, easier to get into, easier to get out of. I wouldn't recommend it unless you're less than 130 lbs.