zz means two shields (in the SKF world where I reside). 2RS would be two rubber seals, I would think that would be the best bet. Now that I think about it, the rubber shields will cause more friction (make it harder to spin), so two metal shields would keep more crap out of the bearings than one.
If anyone needs any bearing or seal help, I'm always around and willing to help out my boys.
Take care,
Tim