Some very nice suggestion, and a great opportunity!
Regarding their quality, in my experience, the later gloss ones don't shatter and tear as easily as the older (flat) ones and with some help of a good glosscoat before and after can be made to work -but indeed, Fantasy Printshop or Cartograf they are not.
What bothers me the most is the registration of colour, as I commented in the other Roden thread the registration on some items is can be rather badly off. Decals requiring some careful handling I can live with (but, still, would rather not!), but registration issues are almost impossible to correct. Perhaps we can help by suggesting schemes with less colours on top of each other, and Roden could help by separating more complex markings (colour-wise), so we modellers need to lay them on top of each other? I'd rather place the separate red, blue, white or green dot in a roundel myself, then to have to fix one that is printed off-center.
Another suggestion: print the rudder texts separate from a rudder stripe decal, as more than a few people will be painting the stripes.

Getting back on track, my suggestion would be the Allied ace of Aces.
His early S.XIII in particular, with the clover:

For a later one, I've always fancied this spider-scheme that was in the Eduard 1/48 kit:

And another vote for SPA48 and Smith IV
For the Avro, I don't know, as I don't know a lot about it, and for the Sopwith, it is perhaps too soon because we do not know what versions they will be doing?
For the Sopwith, I'd love to see the Mémorial Flight 2-seater one, and for a 1B1 single-seater SOP111, one of which was interned in The Netherlands:

Source: IPMS.nl
Jeroen