Used to live and die by the straight cut, but now, my tastes have changed.
If I use a straight cut, I always have a double-bladed guillotine. Anymore, I hate the single-bladed, because it always seems to crush the cigar against the side of the cutting hole that the blade isn't on, and usually results in the cap starting to unravel (that was hard to describe, but does anyone else get this problem from single-bladed cutters?)
I got a two-pack of punch cutters off CBid that clip to your keychain, and anymore, I use the punch. For me, it doesn't seem to make a big difference as far as how much smoke I get out of it, and I like it because there's less risk of the cap (and the wrapper) from unraveling and the rounded cap fits nicely between your lips.
V-cuts...occassionally. It's not that I love or that I hate it, it's just that I never have my v-cutter on me and it doesn't make much difference as to how the draw, volume of smoke, structural integrity of the cigar is anyhow.