I think it is even.
Toon Link have a very nice air game and diddy can't make us trip so easily. TL can jump and spamm bombs, TL can jump and throw the boomerang, and of course, TL got nice aerials.
TL generally likes to jump and spamm xD
Diddy Kong can put a pressure game on TL if he can't keep the spacing, and like praxis said, dash atack is good and Toon can't punish it so easily (ok, we have nair and bair oos). We can't garb diddy too much, he's fast...
TL can catch the bananas with nair easily, so you diddys should be carefull...
The zair outranges diddy, and can be a nice spacing weapon. And we can use it while holding a banana =D
Diddy will have trouble to kill, and Toon Link too. Gimp is pretty even too, altought TL have the boomerang to make diddy have bad times off the stage.