Shape English
Ideally this is what I try and shoot most of my shots with when addressing the cue ball.   This allows me to shoot more through the center of the cue ball thus keeping my shots straighter to their true execution shot line and still move the cue ball easily.  With just a touch of Shape English you can easily move your cue ball all over the table.   I often see people having a hard time (missing shots) because they are using more Clock English (as seen below) than shape english.

Center English
If your a beginner, you should probably shoot Center English ONLY for the first 1-3 months.   You will realize that you can get to most positions neccessary with proper leave using only center english.    If your a struggling intermediate, you should probably start practicing running ball in hand 9 Ball racks using just center english.    You will increase your game immensely with comprehension of position using Center English.    If you ever feel nervous in play it is very easy to fall back to the basics knowing you most likely won't compromise your shot using Center English

Wide English
When your out of line (or left with a hard shot) and trying to get your cue ball back in a "Easy Shot Line Position" - wide english is another option of play.    You want to be careful to not compensate your shot to much for lack of position with a more extreme Wide English shot.     Your stroke comes more into play now in a Wide English shot.  The Cue Ball area you contact and the speed that you deliver your stroke before impacting the cue ball can make quite a difference.    Varying stroke speeds can cause the cue ball or shot (or future position) to have different outcomes due to spin/speed/rails impacted during shot using Wide English.

Clock English
I also refer to Clock English as Extreme English.  It is essentially hitting the cue ball on the outermost edge to create an extreme angle of spin (generally) after hitting the rail or object ball.  Knowledge and proper execution of this english is very key for those extremely difficult position recovery shots.   I generally only use clock english when I'm so far out of line or been left with a difficult shot and I want to recover my easy run out path.   Ideally when I'm playing well, I will not use Clock English at all because my game will be basic using only shape english.