These days when a new game comes out I'm trying to beat the E4 with an ever-decreasing number of Pokemon on my team. This time, in AS, I had just two Pokemon, Milotic and Cradily. I got lucky with my streetpasses one day and got a Mirage Island with Audino, so I just spent the entire day there. One thing led to another, and before I know it my Milotic was level 100. That would be my strongest my first time through. For consecutive clears, when I needed money and exp, I just used a Rayquaza. In terms of physical attacking power, it would probably be my 6IV Slaking. I don't really use him very often, but every once in a while I like to remind myself how ridiculous his stats are so I'll take him out of the PC and battle random NPCs.