re: Which SEC team is losing the most talent this year?

All are but some are in different situations. The difference will be who you re-load with.

State will have the hardest time I believe trying to replace Dak. He meant more to that team than anybody I can think of. Ole Miss will is gonna hurt from Nkemdiche, Tunsil and Treadwell. Huge losses there.
I think Florida or UGA probably comes out ok this year as far as losses.

Other than that everybody is pretty much the same.