Leatherman Skeletool is the sweet spot for me, and I have tried bigger and smaller options.  
Specifically I prefer the Skeletool CX plain blade.  The CX is the lightweight version.  They have models with partial serrated blades if that's your thing.  The blade is easily deployable with one hand, altough I put one of these on it:


It has a double headed bit in the driver blade, and an on board slot to carry a second double header, so you can have, say, two different phillips head, a standard screwdriver blade, and a glass breaker.  

Gerber Center drive.

It's in a pack and not on my plate carrier or belt since I don't "use it more than anything else" so it's not on my person. Reduces the weight I carry on kit everyday but will be there if I need it. I've only used it a handful of times (for the driver and pliers) the past few years since I've had it so it's not worth the extra weight to be carried on body daily.

What I do use more than anything else is a SOG folder clipped to my pants pocket that is used for absolutely everything. Kabar tdi on my battle belt as a last resort knife. And a microtech ultratech on my PC for shits and giggles.