The classic trifecta is 7.62 can, 45 can, and 22 can.
That will cover most everything (yes, I know but the majority of guys are running 50AE or 450 Bushmaster).
22LR is fun and cheap, but not defensive or used for most hunting applications.
45 cans are fun and 9mm subs are quiet, but not overly practical (won't fit in bedside safes, hard to carry, make a handgun bulky, but good for home defense if you can just leave a pistol sitting out in the open).
7.62 cans make obnoxiously loud rifles tolerable for hunting or defensive use, and are probably the most "practical" as far as suppressors go.
Strongly, strongly, strongly look at a 7.62 can over a 5.56 can. Once you hear 5.56 with a can, you probably will want to build a 300 blackout. Honestly though, buy whatever you want the most. No one ever stops at "just one."
I would personally go 7.62 first, then 45 can, then 22 can. After that, dedicated suppressors to what you feel you are lacking with your own firearms collection. But ultimately, it depends on what you shoot most, and what you will enjoy--- advice for buying cans is like advice for what woman to talk to. There are some obviously "uhhh.... no, don't go there" but most good ones really boil down to just personal tastes.