This is fantastic!
In my experience though, I found 7-4 to be the level that offers the fastest reset of the Wanted:Monsters mission. Compared to 8-7 that only offers 11-13 monsters, 7-4 offer 14-15 monsters.
7-4 also offer the most Purple in my experience. The boss level always have 2 green monsters so take it away from the total of 14-15, 7-4 offers a 12-13 purple monsters.