Saeviomagy
Adventurer
You could just build the 14th level characters in as straightforwards a way as possible. Stick to static benefits from feats (toughness, durable, weapon focus etc etc). Choose powers that have defined niches (this is your power to use on one big guy. This is your power to use on lots of small guys. This is your power to use when you're low on hitpoints) etc. Try to choose dailies that are just bigger and better versions of the encounter powers that you choose. Avoid anything that requires positioning or use of complex tactics(rogue is NOT a good pick unless your players have already played earlier editions of D&D and understand tactical movement).