Many times when golfers are putting poorly, they will look to their equipment. Whether or not that is the cause of the problem is doubtful. It is more likely the golfers lack of belief in the putter than it is the club itself.
Now you see PGA Tour players with long putters, belly putters, two ball putters. All kinds of crazy looking putter heads and grips.
Then you also see things like the "claw grip", left hand low, and God knows how many others.
You see these things so frequently because players lose confidence in their ability, not because they are having equipment issues.
When it is time to get a new putter, there are only a few things that really matter. The most important thing is to pick a putter that is easy for you to line up. Reread that sentence about five times. It is that important.
If you can't line up your putter properly, you can't putt well. Mine has three lines on the top of a fairly small semi mallet head.
Once you have a putter you can line up, you can make the small adjustments required to adapt the new putter to your stance and address.
It is these unique individual adjustments that each new putter requires that spurs on the improvement. It is the result of doing something just a little different than normal.
Sometimes thats all it takes to get out of a putting funk. But the truth is, it's never the putters fault. Keep that in mind before you go out spend a bunch of money on something that will probably not help you in the long term.