Holding a pool cue and getting ready to shoot should always feel comfortable as well as stable. Many new player hold their stick on top of their hand like a bridge holding up a bus and in may cases if you were brought up to shoot like that this can feel very natural the problem with this hold is that it has a higher percentage of moving around on top of your hand if your knuckles are not completely stable. It is much better to hold your cue stick above your index finger and curl your middle finger over the cue stick this will add more stability while you are shooting as well and give you a sure shot no matter where you are aiming. The real key is to bend your arm and preferably on the table so that your full arm acts as a bi-pod or tripod that will add indefinite amount of stability on a pool table.
Mastering this hold will also allow you to work on what is really important in a pool game which is stroke, using other above hand techniqeus will mess up your stroke because you are now shooting from various angle instead of one. Plus with the hand bridge technique shooting over a ball limits your stability and forces you to shoot off your finger tips and will decrease your confidence level if you ahve to mess with it too much while you are shooting on the felt.