That is a good question with a lot of variables. For all-around pheasant work, #6 shot through a modified choke would be my first choice. If you are hunting over a good pointing dog, you might be able to get by early in the season with #7 shot and improved cylinder. With a springer spaniel, #5 and improved modified would be my choice.

If you shoot a gun with two barrels (either a double or an over/under), I would go with I/C and modified early in the year (with #7 and #6) over pointing dogs and sk2 and I/M later in the year (with #6 and #5) or anytime working with a flusher.