Single favorite pocket cutter is the xikar v-cut. The colibri is nice too, but the original xikar is so slim, light weight, acts as a rest, and still cuts great. I have a xikar series 2 v cut too, but imo, it cuts too deep and is bulky and heavy as hell.
I V-cut almost everything thing, but draw the line at perfectos, chisels, etc. So if there can only be one, then go with the Xikar xi series in the design/machoice. (and $) of your choice.

Look for sales on all the cigar sites, especially for unpopular colors. I also do what @Tombstone said and buy branded ones that are on sale (same cutter that says PDR will be much cheaper than one that says Padron).

Pic of my fav that Jesse and Sean referenced