If you want a linguists opinion, this is it: no one can say there is a better Spanish (or any other language in the world) than the other. All of them have their own particularities and beauty and for that reason no one can choose one to be the better in detriment of another. If that happens, that would create a miscomfort in everyone that is not speaking the "best" language and this wouldn't be nice.
What we all do, as Mart said above, is to like or dislike one variant of a language, but this si your own opinion about it and that is all we can do. For instance: my mother language is Portuguese (Brazilian variation), but I love the Portuguese from Portugal as well. I can't understand much the Portuguese from Mozambique, but I still like its sound, but the one from East Timor I don't like that much.
As you can see, this is a particular opinion.