These different putter shapes lend themselves to different putting strokes. If you are unsure of your putting stroke don’t worry about this. Classic blades and heel-toe blades are more suited to putting strokes that take an inside to inside stroke (creating a shallow arc around you).
After the putter head shape, you can decide what type of insert (if any) that you prefer. Many people prefer a soft insert in the face of the club which makes the ball move more slowly on impact. Hard inserts are also available, but this is ostensibly a matter of taste rather than anything else.
As putters are so personal, they come in many different options regarding the shaft length, the shaft offset and the hosel type and length as well as the shaft location.
As everyone is a different size and has different preferences, these can change how you view the ball.
Putter loft is not always advertised with clubs, as it is not a big consideration for most golfers. Generally putter loft is between 1 and 6 degrees. Higher lofts are useful on greens with slightly longer grass, but a loft of around 4 degrees is fairly standard.
As putting conditions can change from one day to the next (as well as your preferences), some putter models have been designed which allow you to change the weight of the putter before the round in accordance with the weather.