Nova for both (or future all 3) avatars would be nice, but that brings a question as to the replacement of the Nova as Mayson special.
In terms of canon designs we're limited:
Miranda class - old design
New Orleans - AFAIK planned as warp-in or map unit
Danube class - Harassment from a runabout armed with Micro-Photon torpedoes
Promethius - planned as map unit. Seems a bit too aggressive for Mayson.
Springfield - according to DITL a forerunner of the Nebula produced in small numbers.
Rigel Class - 3 nacelles + explorer
Rigel Class - Specs this
could be a interesting supply/support vessel.
Aegis class from stock A2 - planned as map unit
Overall the options are limited and I'd like to hear suggestions for
possible nova replacements as Mayson special.
Edit: After giving it some thought, perhaps the Nebula class. Same time frame as Galaxy, but more numerous and adaptable due to the pods. Perhaps a basic Nebula which can be refitted (different versions from the warp-in)