letro is by far the strongest, but strongest does not mean best. its super suppression of estrone is not really a good thing, but if you need near total suppression of E, letrozole will do it
as far as specific compounds. If using dbol or EQ highly reccomend AIFM, its dual inhibition of 5 beta reductase makes a big difference with these compounds.
aromasin or AIFM is good for any cycle, however reccomend that you have letrozole on hand. If you happen to need that level of suppression. Also for any cycle, while not a fan of nolva, reccomend that you have both it and clomid on hand. its good to have options.
and while you may not need it, reccomend at least one dopaminergic (selegiline, bromo, cabaser, etc) on hand.