Two different pros talked about putting in back-to-back sessions at the St. Louis golf expo.
One said that between mallet and blade, you need to find the putter you like best.
The second pro spoke in terms of shaft alignment: slight offset, extreme offset (Ping Anser), and center shafted. She lets beginners hit about 5 to 7 shots with each, and then they usually like one of the three. She also talked about whether you were left-dominant or right-dominat in your eyes: this would also influence putter type and fitting.
Basically, go with a putter you like.