Well, the definition of fun varies from player to player.
I dare anyone to try and get near sdj overall because places like RF, RR and RE for the most part do not have sc/glitches and there is still the balloons and tag which require an extreme amount of patience/skill to pull off a good run. These are not the only things that will make your rank and once you play them enough becomes second nature.
I think I found another one. xD
I was starting off on RE and fell out of the level near the start so there is the possibility of doing flaps under 20 seconds or more. This place like RR are harder to do consistently but sdj has gotten RR down to a science in his 22"66 run. Nothing is impossible but its definitely harder to attempt solid sc/glitch runs as compared to normal race coniditions.