I voted "grow to waist and then trim every three months," though I think I agree more with Spidermom in that you should try to gain length while you trim but that wasn't one of the poll options.

If your ultimate goal is fingertip it seems like the best thing to do is to gain as much length as you can while getting rid of the ends that make you unhappy.

Ultimately it is your decision, so do whatever you think will make you the happiest during the growth process.