Surface3 because the Pro2 is signficantly heavier. Too heavy to use as a tablet IMO. Just make sure to avoid the model with 2Gb RAM!
I guess if you want to use it mostly as a laptop (rather than a tablet), the Pro2 might be worth considering as the weight would be less of an issue and it's probably more powerful. But personally I would get the 4Gb/128Gb Surface3 out of those two