I’m sure you probably know, there is no one of the best anything in fly fishing. There are so many different conditions, variables, techniques, and preferences, it’d be impossible to pick one best fly.
Fishing Flies Assortment by Silver Lake is an excellent collection of inexpensive flies. For those of us who like to get out and thrash the water, but don’t have the money for designer tackle, these are very serviceable.
55 Flies Plus Fly Box. The flies are well finished and quite good enough to lure the finicky finned friends.