I have shot NM rifles with both slings. There are pros and cons to both. Since you seem to be on track for getting a leather, I would offer this advice:
First, learn how to take care of it and keep it in top functioning condition. This year I went to the west coast for a match and an old Marine that teaches the first day "how-to" class spent a lot of time on the care and maintenance of the leather sling. You may need to repair or replace the keepers after considerable use.
Second, the leather sling is more complicated to get the loop formed and tightened on your arm. Practice taking the sling all the way apart and then putting it back together many times. Then practice taking the sling from the "loose slung" position for off hand to the looped position for sitting and prone (again, many times) Make a note of which holes you use for each position.
The web sling is quick and easy, and I can cinch it up to whatever length I need. The leather sling is more comfortable, but does have a slight limitation in setting the length because of the holes. If you find that your perfect length is somewhere between two of the holes, you will just have to make it work. Good luck.