Because of the cue being round, the b cut I'll actually leave you at higher risk for a gap if not cut to just the right size...leaving you to try and stretch the leather to close the seam. A is better to reduce this risk. However, the best cut in my opinion is one where both cuts have some angle...but are parallel in angle....leaving you with an overlapping seam (like you use in wood working), but no chance of a gap. Also this approach gives you more glue contact area on the seam.
This take a little practice to find a good angle you can hold the blade at consistently....but not much harder to acquire the talent than shaping a tip with a razor blade.