Welcome to the Forum!
If flatness is your primary concern then a Bridge hammock is your best choice. Are you a stomach sleeper? Based on what you said about your priorities, I'd give you a list that looks like this:
1. JRB Bear Mountain Bridge Hammock
2. Warbonnet Blackbird
3. Tree to Tree Trail Gear Switchback
IMO, the last two hammocks offer the most room for the flatness of their lie. But, I don't find either comfortable for stomach sleeping. Stomach sleeping is still very much the realm of the Bridge hammock. The Clark system is one of those that you either like, or don't. Makes it a dangerous gamble at their price if you haven't tried one for yourself. Which, is true of all hammocks. Best bet is to get to a hang and try a few different hammock systems.
Sounds like you're on the right track and it seems you've already figured-out a lot of stuff during your research. If it makes you feel any better, my head still spins on a regular basis around here.