I've heard it said that there are only 3 personal
clubs in the bag; the driver, the sand iron and the putter. You might not see why I just said that but the first 2 in the list are gripped, more or less, in the same way. The putter is not gripped like any other club - remember there are all kinds of putter designs and shaft angles. These may require a grip that is specific to that club e.g. a belly putter.
My putter has a short upright shaft, an off set putting face and a really thick grip, maybe over an inch or so wide. You can't really hold the putter in any other way except in the palms of your hands.
What you need to do is develop a comfortable grip that can be repeated time and time again. The hands must work together as a single unit without one overpowering the other and most players tend to try and reduce wrist action in the stroke.
The putting grip is the one thing golfers toy with most of all, but the grip is only part of the equation and it may not be that what is the problem. Most amatuers tend to flick at the ball (the putter face passing the hands before striking the ball) this is quite wrong. Like all golf shots the hands should lead the club face into the ball.
I tend to shove at the ball with my hands others rock their shoulders. I've tried rocking but it's a bit inconsistant for me and consistancy in golf is the name of the game. Remember you will probably end up changing your putting ever 6 months or so so whatever grip or putting method you chose try to make sure that the action is repeatable.
Paul