Which Ben 10 series is the best?

All the Ben 10 series are good. It is nice to have the very first one so that you can feel how Ben's adventures really started, but perhaps you'll find it is not the very best season.

It is difficult to say because there are certain episodes within each season that stand out as particularly exciting. In the end, it's best to watch from the beginning and enjoy one or two episodes at a time. People do this with Dr Who - a series with hundreds of episodes.