It's totally up to you. Whatever works.

Doing it vertically will give you more range in your vibrato and probably more control. If you're getting noise, you might need to work on developing your muting techniques.
Both the left and right hands are constantly muting and deadening strings.

Like, if you bend this note up:

G|--------14b16~~---------|

... you're also muting the 1st and 2nd string with the third finger and pinky on your left hand and muting the 5th and 6th strings with your right hand thumb and palm.

Then when you change notes, you're constantly shifting fingers around so that any finger not being used to play a note is being used to mute noisy strings.