Yes, technically Puerto Rico is not international since it's US-owned (correct terminology? I don't care...), but we can get cheap flights to San Juan.
[Although at $895/night, we will not be affording the W Hotel in PR]
I'm thinking PR could be a wonderful getaway. For another $200 we could fly from San Juan to the Isla de Vieques, which is a small island of PR. It's where the grand W Hotel is located. It has lots of house rentals and stuff. I'm not sure if it would become a necessity for us to rent a car if we stayed on the island. The more pictures I see of San Juan, I know I'd be just fine staying there as well. I'm sure there's benefits to staying on the mainland as well as the secluded island.
We would spend about the same amount on a flight to Madrid as we would to PR + flying to the island. Obviously, we couldn't go to Spain and only stay in Madrid. We're thinking of staying 10 days where ever we decide to go to. We'd most likely spend some time exploring Madrid and Barcelona. I do think it would be fabulous to spend some time in Europe in the winter. There could be the possibility of exploring Portugal, but we would likely need to fly into somewhere other than Madrid since it would be the middle point between Portugal and Barcelona.
Both places hold much appeal to me. I'm utterly obsessed with Europe, and surprisingly adore the idea of going somewhere cold for our winter vacation. I do think we may end up spending less money in PR (especially if we stay in San Juan), and since I'm a budget traveler, that's important. So send me your tips, advice, etc. on making my decision and any places you've visited, stayed, in PR or Spain.