There are three main types of putter head design:
blade, peripheral-weighted and mallet.

Blade putters traditionally suit players with straight putting strokes. 
They typically favour hard, fast greens and require more of a delicate touch.

Peripheral-weighted putters (or heel-toe weighted) are the natural evolution of blade putters. 
While still delicate to use, they are longer and thinner than blades at address and feature additional weight in the heel and toe for greater forgiveness.

Mallet putters are the most forgiving putters as their deep head designs give them a lower and deeper centre of gravity to improve performance on off-centre hits. 
They also employ various alignment aids and shapes on the head.


Blade Putter
A blade putter has a simpler design than a mallet putter. Unless you're a new golfer who purchased a mallet putter as your first putter,
 it's highly likely that you have used a blade putter at some point in your life. This putter gets its name because it has a straight, 
blade-style clubhead attached to the end of the shaft. The shaft attaches either to the heel of the blade or closer to the center of the blade.

Mallet Putter
Mallet putters have more elaborate designs and are notable for their large clubheads. 
Although the clubface of a mallet putter is square like a blade putter, mallet putters have large clubheads that come in various shapes,
 such as square, semi-circle or even more abstract designs.
 Much of the weight of a mallet putter is away from the clubface, providing golfers with a different feel while putting.

Choice
If you're trying to decide between buying a mallet putter or a blade putter, 
much of the choice should be based on how the putter feels and performs in your hands. One of the key characteristics of a putter is its feel;
 it should be easy for you to swing so that you can concentrate on the putt itself, rather than the putter.
 Mallet putters often have more forgiveness in their clubfaces, due to the placement of weights. Despite their larger size, 
mallet putters are often about the same weight as blade putters.

Swing
Each style of putter is more suitable for certain styles of putting strokes. If your putting stroke is straight back and straight ahead, 
a mallet putter is ideal because of the club's center of gravity, which is toward the back of the club. With this design, 
it's easier to keep the clubface square. If you have an inside-outside-inside arc in your putting stroke, 
a blade putter is better because this putter is easier to twist slightly during the stroke.


More about golf putters :
 
 blade putters, 
center shafted putters, 
futuristic putters,
 mallet putters, 
offset putters,
 onset putters, 
face balanced putters, 
toe weighted putters, 
insert putters, 
milled putters & cast putters