In reply to An Triubhas: I'd say that the South Ridge is a walk. If you want to call it a scramble then it would be Grade 0.25 or something by the easiest line. Of course you can make it a scramble by climbing on the numerous craggy bits, but there isn't an obvious scrambling line as far as I know so it would be more 'playing on rocks' that sustained scrambling. I'd have no hesitation in taking someone with adequate fitness and a good attitude up the South Ridge.
The North Ridge is a little different. It is a much finer route, but has far more hazards for the nervous beginner. It would really help if you had done the route first (I'm assuming you haven't since you are asking) as one of the main dangers on Tryfan is ending up somewhere you don't want to be. The main reason this happens (and this happened to me the first time I did it, and I have seen it happen to others) is that a nervous beginner gets to a steep section and thinks 'ooh er, that looks like a rock climb, I'll follow this path around it'. The place this tends to happen most is at the North Buttress where you transition from a 50/50 mix of rock and path to more sustained (and occasionally steep) rocky scrambling.
As a climber I'd have thought you'd be well equipped to find the right route, so then it's really down to your novice. Are they scared of heights (not really much of an issue on Tryfan, but some people do freak out)? Are they confident moving on rock? If not, then stick to the South Ridge.