Finding the best putter for your game is part art and part science. The best putter should help you improve your performance on the green- that is in speed control, start line consistency, and alignment. Unfortunately, many players use a putter which hurts them in these skill areas. A good fitting is one where you walk away with a putter that is helping and not hurting your game.
With that said, good putter fitting starts with getting the “Big 3” correct: Length Lie, & Loft. A putter that is the proper length and lie angle will allow you to stand with correct posture that allows you to see the target line accurately. Proper length and lie also will allow you to best move your body for your stroke, depending on your grip type and stroke style (hands/arms powered, torso-driven, brush-stroke, etc). Getting the loft of the putter correct allows for the best speed control and ball roll possible. Loft should be fit dynamically as you want to have about 2 degrees of loft at impact, for the majority of green conditions. Being able to try a putter indoors and out is the ideal scenario for the best putter fitting process.
Finding a quality putter fitter in your area is key. He or she will be able to fit any putter design to these three key principles. Additionally, a good fitter will be able to recommend further customization choices, such as grip type & size, putter head design/ CG placement (blade, mallet, etc.), face material, alignment aids, head weight, swing weight, total weight, shaft material, and toe hang. Finding a fitter who utilizes technology in the fitting process is important, too. A high-grade technology such as SAM PuttLab, CAPTO, or Quintic provides both fitter and student invaluable insights into stroke performance, and allow the most accurate fitting to occur.
Putters are still one of the least fit clubs in many players bags, yet they normally are used for the most strokes per round of any club. Spend the time to get a quality putter fitting and you will reap the benefits on the greens.