Once again, go to "The Corner". For the same reason that it's simple, but also because it has four or five chandeliers so there's plenty of room for error. Also once again, just bunch people up under the chandeliers with tar traps and keep blowing them back with the wind belt until you get a suitable crowd, drop the chandelier (don't worry, the game's pretty forgiving with it's spacing), sell the tar traps and move back to the next chandelier. You should get about 15 with the first one, so this achievement should not be a problem.
The level "The Stream" has also been recommended because it has more chandeliers, though the structure and layout is a lot more complicated, the spaces are wider so it's harder to bunch the enemies up, and the chandeliers are higher making the time harder. People have also said they haven't been able to get the achievement on this level despite killing 20 enemies. Still, having an alternative is always good in case you're having a problem with The Corner.