I use the line/label on the ball.
Here's what I know:
When used only "once in awhile", lining up putts with the label or a line on the ball makes things worse - much worse - because 99% of golfers out there have terrible aim with a putter. When you line up the label once in a blue moon and align the putterface to it, most golfers just can't believe that they are aimed correctly, so they compensate for their new alignment (consciously or uncounsciously) but their alignment was actually correct for a pure stroke, so the compensatory move leads to more missed putts.
I know. I was one of those golfers for many, many years. I stood over 3 foot putts and had no certainty where I was aimed. I made more putts without the line. I used to position the ball so I didn't see any markings on the ball - all I wanted to see was a pure white dimpled ball looking up at me. I wasn't what you would call a good putter, though, especially for my skill level.
Last golf season I made a modification to my putting routine. I decided that if I missed a putt, I wanted to know a.) was it a bad read b.) was it a bad stroke c.) was it bad alignment. d.) was it bad speed
I could immediately remove option c from any and all missed putts if I knew exactly where my putterface was aimed before I hit the putt. The only way to do that is to line up the label with your intended starting direction, and to do so precisely, with discipline, every time. Your body becomes accustomed to the new, correct alignment.
You can watch the label on the ball to determine if there was any "wobble" on the roll of the ball. That way you'll know if you didn't strike the putt purely. When your objective becomes to "put a good roll on it", your stroke evens itself out, compensations are eliminated, and pretty soon factor "b:" from above (bad strokes) are eliminated.
Assuming you get a pure end-over-end roll with the label on the ball, the only way you can miss a putt is by not hitting it the right speed or misreading the putt. You willl, over time, become better at reading greens (factor "a:" from above), because you will know exactly how you were aimed before you struck the putt, and then you are getting usable feedback on every putt. You are not left guessing which of the four factors (a, b, c or d) led to the missed putt.
When used on EVERY putt over the length of a tap-in, the line becomes theraputic. You can have confidence in knowing that you are aimed correctly for your intended starting direction, and it frees up the golfer to focus on speed.
It has helped me immensely. It wasn't easy at first, but I stuck with it. I use the line / label on the ball on every putt now. I am a consistently good putter now.
I didn't make this stuff up - it's all in the Dave Pelz putting bible. Knowing where you are aimed before you strike a putt is paramount to becoming a better putter. Even though I don't putt with a Pelz straight-back straight-through stroke, his thesis is correct - you cannot become a better putter if you don't know why you missed a particular putt. You will forever be in compensation land.
P.S.
Just about everyone on tour does this. The next time they show Tiger's putt from the
72nd hole at last year's US Open, look for the true end over end roll of the label on the ball.