IMO the MR-2.
The R model is just a reciculating variant. It's almost exactly the same skimmer except you use a decided pump to close loop the skimmer. It can give you better performance, but keep in mind that the additional price tag of the skimmer is only half of it. You also need two pumps, or a return pump with enough power to "T-off" the return line to feed a skimmer loop. One pump is the recirculating pump, and another pump to push water through the system.
Recirculators are good if you have one very large main pump. For example, I'm looking at a recirc Deltec for my reef project because I am planning an oversized pump (Sequence Dart) as my main drive pump for the whole tank, with a manifold that sends water to my returns, skimmer, fuge, chiller, reactors, etc. This setup does not work to drive a standard Beckett like the MR-2 because the foam head requires quite a bit of pressure to work right. That's where the skimmer's dedicated recirculating pump comes in.
However, if you are already planning on a dedicated pump for the skimmer, just get the plain MR-2 and use a Mag18 or a smallish Iwaki/GenX, etc pump to go on there and you'll be good to go!
BTW, consider using a Mag24 or an Iwaki 70/100 or so and buying the extra foam head for it. It will be a worthwhile upgrade.