Wire or Rope Luff
A wire luff has the advantage of being dimensionally stable over time but can ''saw'' through the luff tape and can discolor the luff when chlorides in sea water attack the wire. If you choose wire, DO NOT consider a vinyl covered wire!!!
A rope luff will eventually shrink due to repetetive loading and therefore needs a good method of *external* adjustment. If the boltrope is provided with no means of external adjustment then discuss with the sailmaker to provide extra length of boltrope so that when it does need adjustment later on, the luff does not have to be fully disassembled to do so --- ie.: simply cutting the sail-twine attachment and having enough boltrope (in storage - so to speak) to provide enough rope (in storage) to get you back to the original length dimension, then resew with heavy twine, etc. With a rope luff sail it is fairly important to precisely measure the "as new" luff dimension so that you can reaadjust/resew later on when the boltrope inevitably shrinks.
My personal preference is: rope luff ... and for long distance/voyaging is either one with an externally adjustable luff rope that I can alter for the ''long term'' conditions so that I can optimize the shape for that particular term; OR, a non adjustable bolt rope but with a cunningham cringle built in a few feet above the tack ... knowing that in a year or two that I will have to release, reposition and resew the boltrope (If I put in extra (stored) length in the first place). The cunningham will allow for precise luff entry shaping and will will be a great advantage when sailing inshore and you need/want a flat entry / high speed sail (no tension on the cunningham).
Sooooooo .... consider a non-adjustable rope luff (but with extra rope already in place to readjust later) and strongly consider to add a cunningham cringle for vastly better shaping potential. Have the sailmaker show you in laborious detail how to ''ease'' and reposition the bolt rope later on; and, buy some waxed sailmakers twine, a palm and stout sailmakers needles to make the readjustment. Definitely have the sailmaker tell you how much ''pre-load'' he/she has designed into the original boltrope in case you have to entirely replace it --- typical ''preload'' (shortening) will be in the range of 1 inch for every 9-10 foot of luff length.
Without periodically readjusting the boltrope as it shrinks the luff will shorten dimensionally which will cause the sail to become too rounded in luff shape and too full in draft while corespondingly tripping the leach while moving the draft rearward. If you can readjust the boltrope length you will restore 90% of a sails shape. If you dont feel that you can make the adjustment yourself, at least be absolutely sure you have saved the original precise as-new luff dimension so that any sailmaker can quickly and accurately restore the shape.
Hope this helps.