I suggest you usethe searchfeature of this siteto find multiple threads in the last couple of months which address your question. Ijustdid a search using the term "best load", limited the search to the turkey hunting forum, and it returned 300 posts.

Basically there is no "best" load. It all depend on your gun, choke, anticipated range, cost, whether you wish to use lead or alternative "heavier than lead" loads, etc. You have to spend time and $ finding out what shoots best in your gun. To my knowledge there are no shortcuts.

My Mossberg 835 with a Star Dot .690 ported choke shoots Heavy 13, 3.5 inch, 1.75 oz of #6 best. Your experiences may vary.