Hi, pretty open queation there, But i believe the best calibre you canhave is one you can confidently place the kill shot with at a range you are capable off,
example, why buy a 6.5, 243, 22-250, if you cannot consistantly place a shot with these calibres at a distance they can accurately shoot at...
start small .22lr keep the ranges sensible, and progress from there, if you are seasoned in the 22lr look for a 222, 223, 22-250 and practice to a range you intend to shoot at until you can call the shot.... then go on the hunt for foxy.... i spend more time paper punching t