I personally enjoy 2 boxing because I use 2 machines and treat them as separate characters. I have run different instances on both characters at the same time and it has been fun and challenging. You don't HAVE to 5 box to have fun. 2 Boxing gives you the edge you need for quests or mobs that you just can't solo and wish you had someone to heal you. Whatever works for you and provides you with the most fun is what you should choose though.