The only really fun Johto fillers were the ones about Team Rocket or heavy on battling. Everything else was terrible. I agree with those who say Team Rocket, "saved" many of Johto's fillers, because back then they were literally the only good thing a terrible episode could have to make it interesting.
That being said, DP's fillers weren't great either, given the heavy emphasis on training. I can see how that bored a lot of people. There were some gems like Spiritomb and Togepi though, but DP's better episodes tended to be the plot centric ones.
Hoenn's fillers could be a mixed bag, as some were very similar to Johto fillers, but others could be ten times funnier and more memorable. I suppose the only reason Hoenn's fillers aren't as hated as Johto's is because:
a) There was a lot less of them
b) The main cast and their pokemon was more interesting
That being said I do agree Hoenn's fillers could be hit or miss, and there were some stinkers...the ones about Relicanth, Huntail/Gorbyss come to mind.
BW's fillers are sometimes fun, sometimes boring. Not much to say there.