I usually hate it when people ask this sort of question, but my brain hurts.
I have both a 250A and a 400C sitting here. Both are matching numbers bikes, with unmolested frames, and no obvious catastrophes.
But there's only one lot of road gear, only one decent seat base, etc. So I can build one into a decent resto that will go onto club rego, while the other will still be a rideable bike, but will be a roughy.
If you were in my position, which one would you focus on, and why?
The 400 is currently more complete, and logically is the one to choose.
But my heart is with the 250 (not that I have any particular emotional attachment to either of these bikes).