question for the guitar guys

talking to the guy who's going to do my re-string for me, he's recommending a medium style string.

I am looking for something which lasts.

I play roughly an hour a night. I'm self taught on a lot of things, but taking some lessons for others, more advanced than I can wrap my head around just trying to pick up on my own. That's the reason he's recommending a medium string.

As for the guitar itself it's a six string Infinity.