Strengths: 1v1 fighting, damage vs champions, assassination
Weaknesses: Lack of range means no teamfighty. You'll get killed very quickly, and you have no AS/AD steroid like other DPS carries.
Strengths: Earlygame domination, usage of all skills, Wild Card poking in teamfights, backdooring
Weaknesses: Less damage output in 1v1, building enough AP to backdoor means you will go down in 2 seconds if they teleport in.
At higher levels, AD TF is less useful due to people running away whenever they see the ult, or being more aware of the map/cooldowns and not walking solo when TF's ult is up.