25 years ago when I asked my turkey hunting mentor which mouth call he liked best, he said whatever was on sale at the end of the season. I resisted his advice for a while, but now follow it. As a matter of fact, I have killed more turkeys as time went on (hint).
As far as slate calls go, I like a slate pot and a glass combo call (or 1 of each). Strikers, in my opinion will make all the difference. Get a few different kinds (tips).
To round out what calls I carry, I have a custom box call too.
I used to carry a variety of calls, but now limit myself to a mouth call, pot call and box call. I could easily get by with just a mouth call.