Since Latin America is bigger than Spain and has bigger economy, population, what variety of spanish should I learn?
Gonna depend on the things you want to do.
Movies and TV series: You usually gonna find only two dubs, spanish from Spain and neutral latin. Spain usually dub more material than latin America but there is a big war about who does the best dub.
Literature: It's not much affected by the country, because you don't read the accent, so you probably not gonna have any problem with that if you know spanish from any country.
Talking and traveling: Here starts the hard part. You better learn the variety of the country you gonna live or if you only want to talk with the immigrants of your own country, learn the variety of that people. You never gonna sound native, so I recommend you learn spanish (in general) and when you visit one new country, just study the little differences you gonna find there.
When I started to learn English, the pronunciation was a big barrier to me at the beginning, I couldn't understand why Americans and Brits pronounce the same words differently like in "aluminum". I couldn't understand it cause we don't change the pronunciation of the words, we only change their intonation (accents). So it is not that much important as you have the same "phonetic transcription" for every single word - you don't have to, like in "aluminum", learn two pronunciations for the same word.
And as a personal advice I will recommend you to look for the accent or culture that you like the most and enjoy it cause this way you will learn more (the more you like it the more you learn it).
La RAE (Real Academia Española) is the most mandatory and official dictionary within Spain - it kinda has the last word, if you want to be orthodox with your learning. In Argetina Spanish changes a little, but anyways it's almost the same. I have the impression that Spanish from Mexico is the most representative variant in Latino America.