M14 type rifles are known to be hard on scopes so a quality piece is preferred. Now to specifics: for general use I often recommend a Bushnell Elite 10x as being the value buy. Very good scope, fixed power of course with a 1" tube and exposed target turrets. Only real downside IMO is the reticle being a bit too thick; now for hunting consider a 3-9 variable - I have a Zeiss Conquest on one of mine and, again, it is a quality piece of glass that certainly does the job of being a good choice for hunting. For target work I like LOTS of magnification but the M14 poses a problem in that a large scope really affects user ergonomics (and even a Coyote cheek rest has limitations) so some of my favorite scopes (like NF NXS) never feel right on these rifles. A scope that does work well is the Leupold Mk4 as it isn't too large (only 50mm objective) and still has good magnification ( mine is 8.5-25 ).
Of course you didn't mention budget and so in the above answer you have a $250 $600 and $1800 solution