I'm student currently studying in Florence. I was wondering what option would be better taking a train or flight?
Fly on Vueling. The distances are somewhat deceiving across France and Spain.
I flew RyanAir from Bologna to Seville for $97 including a checked bag in February.
In addition to Florence airport, Pisa airport can be a good choice for budget flights, or there's also Rome. Vueling is a likely suspect or www.skyscanner.com is a good search engine for more options.
As said above, flying will not only be much faster (particularly if your target is southern Spain instead of Barcelona), but cheaper. To find flights, use Skyscanner: http://www.skyscanner.com/
Do look at flights from Florence FLR, Pisa PSA, and Bologna BLQ, as all of them are close enough to Florence to use if you can get a better deal or route. Rome FCO or CIA are farther (and take longer to get to, with no "one seat ride" options), but will have even more options.