Mwahaha! Watergate
The defaults are probably NOT good, at least not for attack and release. I would suggest starting with attack around 200-400 ms, release at 2000-4000, and make sure that Exponential Release is disabled (you can enable it but we did our tests without it). The default value for new settings should be ok.
3 people (including me) have been testing during development, 2 of those have tested without an AGC, just the multiband by itself at infinite ratio and a massive (40 dB) drive. If you do that, you probably want to use band linking with at most 3-6 dB between bands.
I can post my own test settings here, but I don't want to push everyone into using it the same way. And my own settings were made more to see if things didn't break than to actually sound good. Others have done that, but I don't want to post their not-yet-completely-finished versions here either. What I can tell you is that people have reported that they need far less "tricks" such as equalizing settings to make everything sound good; the new compressor delivers a much more consistent output. So if you start with an existing preset, chances are that you have to disable a lot of "enhancements" elsewhere.
(Which reminds me, I need to add an image to the blog post that shows the improved consistency - doing that now).