I guess 4. Some of them are good, but especially a lot of the evolutions of older pokemon are not only ugly, but uncreative as well. Also, the fact that so many of the new pokemon were evolutions of older pokemon is quite uncreative, as they had something they already created to base the design on.
Gen 5 was mostly quite creative. Few truly generic pokemon, but they are there. Some of the ideas are maybe weird, but some concepts are great imo, like Pawniard and Bisharp being based on chess pieces, very creative. Pokemon like Scrafty and Darmanitan are great as well.
But it's true what the above posters say: every gen has creative and uncreative pokemon. So the question is, should creativity be based on concepts or design? Because concepts eventually become more difficult to come up with (which is why things like ice cream cones and trash bags are used), but the actual design of the pokemon can still be creative.
Gen V is the worst when you look at: Woobat (which rhymes with Zubat, so that's a lazy name)
Roggenrola (which is essentially a faceless Geodude clone)
Patrat, which is almost the same as Sentret (a rodent that keeps watch for danger)
the ugly*** Timburr and evolutions
Sawk and Throh, which are basically Hitmon-wannabes
Cottonee (lazy name)
Gothita and evolutions (we already have Jynx for creepy female Pokemon)
the awful pun of Foongus Amoonguss,
Klink and Evolutions are just lazy and BORING BORING BORRRINGGG!!!!
Vullaby has got to be the least appealing Pokemon of gen v. Yeah, that's what the fans want, a vulture wearing eggshell diaper. --- Bazinga! *dives into ballpit* Pokemon Black Friend Code: 0605-2800-9952; Trainer Name: Solace; First Pokemon (roleplaying): Shiny Umbreon