Ginga Tokkyuu Milky☆Subway

The Japanese voice acting is very natural in both of these. The cast members interact and talk over each other like people actually do in real life, and they're really funny too. Tesagure was made with MikuMikuDance so the animation quality is terrible, but the things they come up with while ad-libbing are hilarious. Milky Subway has a similar vibe, the humor is a little more scripted but has excellent flow. 

Both are sci-fi short shows about a distant future where characters tend to have casual, often non-sensical conversations with each other.