it's honestly getting a little difficult to tell, because there are quite a few high capacity diapers available now. There are numerous varieties of the comficare design, and they have differnet cores, different liners, and different shells. The shell and padding shapes, elastics, and tapes seem to be the main consistent things. But with the others changing, core composition and top sheet in particular, they can get hard to compare. Is a diaper higher capacity even if it has poor wicking and tends to leak before full?
But yes I think most will agree with the general opinion that the comficare design diapers are the current kings of capacity.
The Forma-Care X-Plus are medical diapers, and not as bulky as the Comficares, but they fit better and have a crazy absorbency. According to Save Express, the mediums hold ~4.5 litres, and the larges ~4.8 litres. But other sites say 3.6l and 4.1l respectively :-/
Probably not quite as capacious as the Comficares, but I find the Comficares tend to leak round the leg cuffs, so the Forma-Cares probably hold more in practice (on me, anyway).
I use both Space Diapers and Comficares. They are neck and neck but I think the Space Diapers may have an edge. Space diapers have better tapes, no comparison. They are identical fitting diapers and obviously cut on the same machine. I take that back. Space diapers have nice taught elastics in the middle, so they make a better fit.
No other two diapers have this capacity.
The current style Comficares are discontinued. Rearz.ca has a diaper like the Space Diaper and I heard Space Diapers recently made it to Europe.
If you like Comficare, The Space Diaper is a better version of that, if you don't mind the ABDL theme.
Rearz.ca will have a white version soon and maybe Abu will too.