Hmm. If I could only own 3 rifles (I'm assuming we're talking centerfire limitation only else I'd have to rework this to include a .22lr

)
I'd say the best 3 (if you could only have 3) would be:
.223
.30-06
.375 H&H
Ironically, I only own the .30-06 out of the above

. My personal (sporting) rifles consist of:
Winchester 670 in .225 Winchester
Turkish Mauser in .257 Roberts
Sweish m38 Mauser in 6.5x55 Swede
Savage 110 in .30-06 Springfield
Springfield (Remington Mfg) 1903 in .30-06 Springfield
La Coruna Mauser in 8mm Mauser
Also have a number of original condition milsurps but they don't go out hunting with me

. And I realize that it is a bit odd for a milsurp collector to have as many "sporterized" rifles as i listed above, but only the Turk was done by me (and it was a $40 rust-bucket with missing parts

). The rest I just "saved". I've a soft spot for sporterized military actions

.
Reason for the above is that all I hunt (with a rifle) is whitetail so I've just not had a need for anything outside of whitetail cartridges

.