Rask will likely come over to the AHL next season and need a year or two of seasoning before making it to the bigs. Montoya will already have 2 years experience in the A at that point and should be ready for the NHL next season.
In terms of the better career, it's a toss up at this point. I think most people would say Rask has a higher upside but until he comes over to North America and shows he can play here, it's hard to pick him over Montoya.