Most manufacturers these days have some sort of skill rating system that they mark on their boxes, Airfix was the originator of that idea I think and several others, including Monogram-Revell have followed suit.
By far, Monogram Revell offers the best balance of value to money and workability for less experience modellers. I've always found Monogram kits to be quite forgiving of beginers mistakes.
You might also want to try Revell Germany's line up of kits, they have a wide variety of kits to satisfy beginers and advanced modelers, they also hold the molds for most of the Matchbox line of kits and do release them under their own label from time to time.
I don't do auto kits, but I've been doing aircraft for over 20 years, I started when I was 7 and I can say this much for my experience:
Monogram-Revell and Revell Germany kits: good range of kits for all skill levels and skill levels are marked on the outside of boxes.
AMT kits: I wouldn't build another aircraft kit from these guys if you paid me.
Italeri: Generally alright stuff but a bit inconsistent, not for the beginer, but something to look at when more experience is gained.
Airfix: A bit hit and miss these days, kits come marked with skill levels on the box, but once you get the box opened, you could sometimes argue the skill level they should be for. Better for the modeler with a bit of experience.
Matchbox: I would recomend any matchbox 1/72 kit to a beginer, they're quick and easy and generally good representations of the real things. They hold the shorter attention spans of younger modelers well and give them something to take pride in. The only drawback these days is that to find old Matchbox kits you have to do some research into the Revell Germany product line.
As a last note, stay away from Eastern European kits of any brand. Many are very good quality, but from what I've seen, none could be recomended to a novice modeler.