Better Design Than Aliens
I went with Zeroes over all other options because at the time (Alien recall, pre-Mastercam) they were the only single-stem microcam on the market from a top-end manufacturer. In deep, parallel cracks, or in horizontals, literally any cam that fits in the placement will do. However, in shallow, vertical placements, you need flex both perpendicular and parallel to the cam's axles to make sure a fall won't completely lever them out. Thus, zeroes over C3s and TCUs. Since I've owned mine, I've come to prefer them over Aliens, since you've got individual cam manipulation (which makes them much, MUCH easier to clean). While they also have that advantage over Mastercams, I personally don't like the sizes of Metolius cams which is why I never really considered TCUs or later Mastercams. That's an issue of personal taste though, so buy accordingly. I still prefer the larger per-unit range of the Aliens, but I understand why most manufacturers are loathe to use such a large cam angle on such a small cam.