Its really whatever you want. The ball is pretty inexpensive new, so if the drilling on the 2 used ones isnt going to work, you would have to pay for the ball and then pay for plugging and redrilling.
As far as weights go...thats all up to you. SOMETIMES when people use lighter weights they think it will not hook as much when it fact they may actually get more hand into the shot and have a harder snap. For me, I do usually have my dry lane ball a pound lighter---just what Im comfortable doing.
I guess if I were to choose one of the used ones, I would choose the 15lb. Throwing NOTHUMB does have its advantages too. If the fingers are even close to fitting you could try throwing the balls before buying them, just to see if they will work for you. Now if the ball is owned by a lefty and youre righthanded that wont help you. But otherwise, you could at least compare it to your current stuff and decide if you like it.
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