Well, both Pokemon are definitely quite good.
Florges is the Pokemon that has the highest base stat total. Florges has an incredible Sp. Def stat! Like, it's Sp. Def could easily be considered legendary. It's also got an incredible Sp. Atk stat, but everything else is rather mediocre. Florges is definitely your go-to for a bulky Pokemon. Gardevoir is very similar with great Sp. Atk and Def. stats with the rest being mediocre stats.
Gardevoir wins the moveset match, knowing a fair few Psychic and Fairy moves, while Florges doesn't learn many (their pre-evolutions learn them all) - both of them don't learn many moves through TMs, however the winner would still be Gardevoir in that case.
I guess it really depends now - both of them have nearly the same stats, if you want a REALLY bulky Pokemon I'd recommend Florges - if you want a dual-typed Psychic as well as Fairy Pokemon with a Mega Evolution, I'd recommend Gardevoir. (I feel so biased saying all that stuff about Gardevoir, since I just love it. xD)
They are all first available at Route 4, but surprisingly Flabebe has better stats that Ralts, so this might influence your decision.
Have fun deciding, I guess... xD If you want any more info, you can just ask me.
Hope I helped. :)