It's all depends on what you like. That being said 4300k will put out the most light. 6k and 8k are basically all about color of the light being outputed. 6k and 8k will put out less light. For the most case 6k having a blue tint to it, and 8k being purplish.
I had 8000K and they weren't purple, they were blue, very blue! Actually look at the above banner, if its a yellow IS300, thats my car, perfect example of how 8000Ks look. The only downside is its a bit more difficult to see in the rain.