I do have my brush that I prefer, but all the others, or most of the others, I obviously like for their own different reasons. The days I decide to just grab a quick face lather to run run out the door are perfect for the smallest brushes.
In my opinion, it's not a waste if you're using a brush that makes you happy.
I use my brushes in a sort of rotation, though there are some brushes that I reach for more frequently and others that get little use. I rarely will use the same brush for two days in a row unless I'm traveling. Like to mix things up. The exception is if I have a new brush, in which case I'll use it more or less exclusively for a while until I've gotten to know it.
I had what we commonly call here the "SBAD", trying nearly every major brands available around, but came to sell all except two: a Mühle synthetic and a Plisson white two bands... I don't really rotate everyday, but after a couple of months usually...
I only own three and two are identical in all but handle color. All are Omega boars, two are B&B specials. The B&B are my preferred model, as they are just the right size for me. The third one is a '49, quite large. It is my travel brush. I'm breaking in the pink B&B, and it's tied for favorite. I'll probably use it nonstop for quite awhile.
I use my Omega boar just about every day. I have a Whipped Dog badger but I only use it about once every other week or so. I just prefer the feel of the boar and I really like consistency over variety so I'm not inclined to rotate hardware. I will occasionally rotate between soaps or creams but I will stick with the same software for at least a week or 2 before switching.