I have a faux-walnut Palio guillotine, one of the aluminum teardrop xicars, and a pair of xicar mtx multitool/scissors.
I rarely use the teardrop xicar, even though I like the design and it has great blades, as it feels clunky in my hand, and I have a hard time getting the cut "just right" with the spring-action working against me. It's also a little heavy/clunky to have riding around in your pocket, but that's my fault for picking up the one with the metal casing.
Blades on the Palio are just as good, and I find it easier to use than the Xi. Also, it has a curvature to the plastic that allows you to rest your stick on it, if you find yourself without a cigar-sized ashtray. It's lightweight, and the profile is slim even in the protective case. I also like the larger-than-average thumbholes, as I'm a big fella with a "mickey mouse-esque" set of man-hands.
But more than anything, I tend to use the multitool. The blades are sturdy, every bit as sharp as the others (which, again, are all quality blades, imo), and I like the smoothness that I can get from cutting with the scissors. Admittedly, the tools on the thing are pretty much worthless, but I'm sure one of these days I'll find a use for the screwdriver. The thing is very small when folded, lightweight, and seems quite durable. They're not great for cutting anything north of a 55rg, but I tend to expect that with any cutter. (As an aside, I regularly see them posted for $25/free ship on
www.cigarmonster.com, where the others tend to retail in the $40-50+ range.)
All of these cutters have great "no-hassle" warranties, and I'd recommend any of them. It's really just a matter of what feels best for you.