Best is pretty subjective. The ones from the major manufacturers all work. If you have a controller, I would get a chlorine generator that is compatible with your controller. Jandy used to support other brands, but the last I heard, the don't any more. I use Pentair stuff, and I can control the generator from my touch pad. I wouldn't use anything else because of the convenience factor.

This may not be applicable to you, but I just wanted to make sure you consider how it fits with the rest of your system too.