I like to pratice both..... my gym used to call it "monkey grip"
months I go w/o thumbs on presses..... then a few months with thumbs....
same thing with pulls.... thumbs.... then for a few months I just "hook" with the 4 fingers.... and pull... ala jay cutler on his pull downs... minus the straps.....
which by the way.... gonna start employing the starps again.... soon, for a coupla months anyway