I use both. I use Kiwi with a range of extensions to block JS and trackers and all that, but I also use bromite for when I need to run something like a web app, it is easier than fiddling with extensions sometimes. Also I get some rendering issues in kiwi from time to time even with all extensions turned off.

Bromite has some great privacy centric features baked in, and google cruft removed. I'm not sure kiwi does. If bromite had extension support it would be perfect.