start with the cheapest, good quality one you can find, like a leatherman PST, or Gerber, SOG pocket-plier, whatever. then carry it for a while and figure out what tools you use, what you would like changed.
alternately look at the things you encounter in a day that a multi-tool might be good for, then decide if a dedicated tool would be worth carrying, ie. I carry a crescent wrench at work all the time, because it works better than pliers for what I do, and it is expected that I have one. Multi-tools are best for those odd tasks that happen, but not often, as no Multi is better than the tool it replaces. Then once you have a general idea of the tools you are looking for, look for the multi that has them, and features you want. (outside opening blades, needle or blunt pliers, etc)
then look at what size you think you'd reasonably carry, if you work in jeans and a heavy belt, then a large tool might be for you, but not if you wear a suit. (again depends on you)
If all you need is a few screwdrivers from time to time, maybe a SAK covers you, if you need very specific tools, maybe a SOG is good where you decide the load-out (as I and others have done) Remember your needs may change, and there is nothing wrong with having the "right" tool for the job so maybe you need a wilderness multi-tool and an Urban one.
Hope I'm making sense