Joker is pure chaos. Riddler is some person with self esteem issues that wastes his time putting Riddler trophies all around the city for me to ignore. If Edward Nigma was so smart he would buy stocks until he would be able to buy all of Wayne Enterprises and eventually rule Gotham City.
In terms of pure entertainment value I give it to the joker. Riddler is up there though. But the joker is always entertaining with what he does and how he responds to things. Riddler is more cool with how he sets things up and how smooth he operates.