I own more decoys than I will ever be able to deploy in one setting. So I have several bags that I keep organized. My "Best" bag consists of about 18-24 mallards, with 6 of those being super-mags, and another dozen pintail drakes I like to use. In this "primary" bag, I can fit about a dozen teal, a half dozen widgeon, or a few goose floaters, based on situation/time of year/etc. This is what I carry the most, and will sometimes pull it down to a couple dozen or less later in the season.
My secondary bag has another 3-4 dzn mallards., and then a third similar bag. I keep a half dozen woodies, a dozen teal, a half dzn widgeon, and a handful of divers handy that I'll sneak into a bag to add some color if I'm feeling groovy.
And now I'll tell you that none of that matters. Yeah, multitudes and masses of blocks are cool, and on the right days, sheer numbers, along with the right conditions are certain to bring in ducks; however it comes down to what thaner said - the most important factors, in addition to the "art" of being in the right place at the right time, of course (aka - scouting) is good calling, good cover, motion... all of those things are as - if not more - important than numbers. In fact, just with decoys, the realism - a fresh coat of paint - can help, especially late in the season. Give me a half dozen big realistic mags with a fresh coat of paint over a dozen or two of K-Mart's finest Flambeau specials any day.
But the bottom line will still be - the right place at the right time! As soon as we think we know what these critters are going to - or "supposed" to do, they do something else!!!!
WE are the ones that think this stuff matters!
Good luck, and have fun with it.