Squirt P4. Have one, love it. As for the choice in general:
1. Leatherman build quality is second to none. I give them out at almost every male birthday I attend, with no complaints so far. Most Gerbers sport fit and finish issues and have been known to collapse under pressure.
2. Gerber keychain tools are significantly larger, with little gain in durability or potency (see 1.) On that point, Gerber tends to produce anemic drivers and weird looking blades. Leatherman makes a point of utilizing every millimeter of available space to the fullest, producing natural feeling tools with solid, proportional blades.
3. Leathermans are assembled in the USA. Gerber outsourced to China, if I remember correctly.
4. Leatherman is a pioneer in the field, Gerber shamelessly rips off its designs year after year. I'm no fan of Gerber, is what I'm saying.
Here are reviews on two of the most relevant tools:
Gerber SpliceLeatherman Squirt P4Finally, as with most such comparisons: whichever one you go with, it'll get the job done much, much better than a no-name knockoff ever could. Both companies are committed to making a quality product and both stand behind their products in terms of warranty.
Hope that helps!