For really being user friendly, practical and cheap enouth that you do not cry too long if it goes overboard, I like the Gerber urban legend semi-serated. Small, but remarkably non-slip. Has a knife blade with thumb-opener and double sided safety release. It also has a pair of really useful scissors, that double as a marlin spike of sorts (or basically that pull-through tool that lets you splice cordage.)
I bought one, lost it and ended up buying eight so that they last me for decades after they go out of production.
My wife prefers a knife called a claw. It is a locknife with a crescent shaped blade that has its cutting edge on the inside of the crescent. Saw edged and very easy to open and use on handed, it makes emergency rope cutting (it can cut lifelines if you don't mind throwing it away soon after) an utter breeze and control is excellent. It even has one of those double safety clips on it, that lets it get clipped to waistband or shirt pocket...and not come undone until you grasp and squeeze it.