I would say Zapdos Over Magneton since there is Magnezone and Zapdos has a bigger base stat. I'd suggest a ground type for that pesky Pikachu of his at level 88. A good place to train is elite 4. I had a team fill of legends but lower level and i used some weaker pokemon for max revives. If you need more, comment.
hope this helps! :D
I will say Zapdos cause hes stronger depending on level. What level is your Mangenton?
I say Pikachu.Just get him level 100. Mwahahahaha! That will be easy since it will not be very effective on the Pikachu's and you will have a stronger one.