I did the 3 peaks challenge last year, Ben Nevis took the longest its not to tricky but just goes on and on and on…. Scafell pike is quickest to walk up I would say, but the route is the toughest on the knees and I had to walk up it at night. Snowdon is the family mountain in my view quite crowded and has one tricky bit and as its been mentioned there is a train but I wasnt allowed to get it 🙂