I have to agree with Fausto here. To me, and my own life style, the 58mm SAK's are the most used. Life in modern suburbia means lots of little jobs for a pocket knife. I've lost count of all the things I've fixed with my little classic. The SD tip on the nail file is a perfect shape to deal with number 2 phillips screws that seem to hold everything together these days. I've worked on a Vespa motor scooter with my classic, as well as Smith and Wesson revolvers, a Briggs and Stratton powered lawnmower, light switches, clothes drier, electric trolling motor, and a lot more. The scissors are great, and the little knife blade cuts twine, plastic blister packaging, and foil seals inside the cap of windshield washer bottles very well. The tweezers have been used to pull small splinters out of me, and a throne or two out my welsh corgi's paw. Even the toothpick has been used for non dental matters. It's fine enough to untangle my better halves gold necklace chains without damaging anything, and you can unlock most police handcuffs with the either the tweezers or toothpick. Just a useful tidbit of info, if you had to.
The classic is small enough to get into federal buildings here in Washington D.C., and the 58mm line of SAK's go onto the Amtrack trains with no problems. They are U.K> legal, and are good for most places with restrictive knife laws. The biggest problem with the classic and the other 58mm's is, they are so small, people tend to under estimate them. They are far more capable in real world use than you would think.
A classic is a good place to start, as it's cheap to buy, small enough to go on a keyring, and if you don't like it, just gift it off to somebody who has no knife. I've gifted many classics, and in a lot of cases, it serves as a gateway drug, leading the gif tee onto more SAK purchases. One thing about SAK's; their tools really work at their intended tsp, and the quality is great. The saw on the Vic farmer is capable of real wood cutting in the boonies, and so the farmer is popular with those who are into bushcraft. You just need to review what tools do you really need/use in your everyday life, and pick a SAK that is reflective of that.