I may well have liked the garmin if I hadn't used the tomtom before. There were a lot of 'gimmicky' things on there that were very good and I did like, it was just the navigatio & maps side of things that I thought were pretty crap.
I would say as you will have only just passed your test that the tomtom would be better. The maps are a lot clearer, there's a lot more going on on the garmin maps which I found confusing, you had to actually look at the map to tell where you were whereas the tomtom only requires a very quick glance. It's a much simpler map that I think would be better for you. ALso the lane guidance on the tomtom is so much better. The lane guidance on the garmin is pretty pointless as it doesn't stay up long enough and it's not very clear, i.e. it only stays up for about 5 seconds and only shows that you have to leave the motorway whereas the tomtom stays up from 1/2 mile away from the junction, is very clear as to what lane you need to be in, so for example if you could use 2 lanes it will show you. It's great when you're on a motorway that you don't know that has confusing junctions. The voices on the tomtom are much clearer too. The garmin voice is very computerised which can be quite confusing with the road names, whereas Jane on the tomtom is very clear.
Also the tomtom gives you directions ahead, e.g. cross the roundabout, 3rd exit, then take the middle lane or in 800yds turn right, (name of road), then 2nd left (name of road). The garmin however will say enter the roundabout, then won't tell you what exit you need until you are on it and then once you're finally off of the roundabout doesn't tell you which lane you need until it's too late, and the other example was turning into my road, the garmin would say in 800 yards turn right, then once you'd turned right it said in 400 yards take the next left, completely missing out the 1st road. Would be very confusing if you didn't know where you were going.
God that makes it all sound like I work for tomtom, I don't I promise. I actually would love to have a satnav other than a tomtom as there are things that others do better and the company seems as though it's now so big it doesn't care about it's customers so I'd love to take my custom elsewhere (especially as our year long live services run out next week so we're going to have to pay them even more money to keep that up and running)but unfortuately, imo noone makes one to compete with the tomtom yet.