According to Skyscanner prices for Costa Rica (San José) are about 20 euros cheaper (183 vs 204) and the cheapest ones are both direct flights from Miami. So if you come from the south it doesn't make much of a difference between the two, if you're based elsewhere it depends, even though Costa Rica seems slightly cheaper. I've never been to either country but I guess Costa Rica is a good start.
RE: I just would like simple advice