As a whole team, I prefer hitting 12 different types. But counting main playthroughs, I suspect the most common ones hit are Water then Psychic. Flying, Electric and Steel probably round out the top five, because I frequently use the starting bird and I frequently used Magneton. Ice is likely quite high as I do recall using Dewgong, Lapras and Walrein a bunch. I would be curious to figure out how often each type is used based on what I remember of my playthroughs, since there was a point I tried to make each team unique from previous runs. Meaning I've used nearly all Pokemon from gen 1-6 to beat the game, barring admittedly most single type Pokemon as I tended to avoid those when possible.