What better 1 group=1 key OR 1 group= many key?

On the one hand - the relevance, on the other hand - an inexplicable approach AdWords Google.

After many established advertising campaigns AdWords, I can recommend to try different ways.

The best solution does not exist.
The solution is always the average, and based on experience.

Good luck, my friends!

If you have solution for this question, please, share with us.