An interesting thread which I seem to have spent far too much time thinking about
Whilst I like Geir's idea of the 5 and 10dT containers as they match the trade and spec lots, I prefer J.L. Brown's 4, 6 and 8dT for a couple of reasons.
The first is that they are close to the 20, 30 and 40 footers we have today.
The second is the mostly aesthetic. I like the idea of taking a 3x3x3 cube and doubling it's length to get a 4dT container, then doubling that length to get an 8dT. You can create "sticks" of containers clamped together which follow the same ratios (and also allow access to both ends of each container without having to break anything apart). For example a 4x2 stick of 6m containers follows the 1x1x2 ratios of the 6m container. (This is 32dT so with a bit of handwaving I'd say a modular cutter could move this stick instead of the standard 30dT cutter module). Making an 8x2 64dT stick follows the ratios of the 12m container (1x1x4).
Using 12m containers gives you a 32-box stick (8x4 256dT) or 64-box stick (16x4 512dT).
If you're OK with only being ale to access one end of each container then blocks of 2x2x2 could be use as the basis of the sticks, which then gets into serious tonnages being moved.
Once you're at that level it might be better to use larger 6x6x12m containers (32dT) and 6x6x24m (64dT) which could be built into similar sticks:
12m containers; 4x2 stick = 256dT. 8x2 stick = 512dT
24m containers; 8x4 stick = 2048dT. 16x4 stick = 4098dT
Basically I like the idea of sticks of containers following the same ratios as the containers themselves, and also being able to access each container when it's not aboard ship.