I used Pikachu in X and Y and I loved it <3.
Pikachu, as a Special Sweeper, can learn great moves like Thunderbolt and Electro Ball with ridiculous Speed. Plus, I never evolved Pikachu (since I'm sentimental xD) and Raichu has great stats, as well. It's a great addition to your party.
Pikachu, unfortunately, cannot learn Iron Tail, however, if you get a Pikachu in BW2 and learn it Iron Tail via the Move Tutor, you can transfer it to X and Y and it can be your new party member. :D
Hope I helped. :)
Source: I played with Pikachu