THis is a trivial one. Forehand all the way. If you cannot hit a backhand, you can still control the entire court if you have a great forehand. Impossible to run around the forehand to hit backhands much the same way. Too much room to make and defend. Of course, if you do have a weak wing, you will be a mediocre player, but that is true of forehands as well. On the ATP, all the best players have dominant forehands. Djokovic was a second-tier player till he made his forehand a world-class weapon. Roger's forehand has controlled the tour for years, even when his backhand was not exactly the most lethal out there.
Another one: Anci > JJ achievements-wise