A few thoughts...
1) I am ok with butterfly clips, but no way in hell will I use a boat snap.
2) I tried the old style ring bungees as well as the latest style ring bungees from Dive Rite and neither one really allows the tanks to ride or trim properly.
3) That was the case with both the old style nomad wing as well as the new style wing that ran the bungees underneath the wing. In both cases the tanks hung lower than I preferred - not as low as bottom clipped stages, but close.
4) On this last cave trip I switched to Edd Sorenson's "old school" bungee system on my Nomad. It's basically a piece of 2" wide webbing about 10-12" long with two grommets on each end to attach a loop of bungee. It slides through the slots for the upper single tank cam bands and is retained by a sex bolt through one of the center holes. The grommets support a loop of 5/16" bungee on each side that is quick linked to a bolt snap that attaches to either the pivot rings or one of the D-rings on each side of the harness. It's purpose is just to hold the bungee in position so you can reach back and grab it (a chicken wing/thumb maneuver).
As noted in the post above, Edd just uses a bolt snap with the eye tied to the tank neck with a loop of gold line. However the system is also easily adaptable to tanks set up for the DR choker system, as all you have to do is remove the choker. You can then clip the upper bolt snap to the shoulder D-ring and after you've clipped in the tail, just slip the bungee loop over the tank valve. The boltsnaps remained clipped, but stay tucked out of the way.
It gives you all of the benefits of the ring bungee system (ability to have the tanks metal to metal clipped to the harness for walking, boat boarding, etc) with the improved trim and lower profile of having regular bungees over the valves. Plus it's a lot easier to clip the tanks on than the ring bungee system as the business end of the bolt snap is not secured next to the valve.
For a Nomad, Edd's solution is pretty slick as it properly positions the valves up under your armpits providing both decent trim and a flat profile.
And it's so easy that Marci can even do it without problems. We rigged something similar for her Nomad JT, but routed the bungees underneath using the webbing on the perimeter of the wing as a guide for the 5/16" bungee, but use the same quick links, bolt snaps and nomad tank set up without the choker.