"Sama" isn't for equals.  It's for superiors.  "Dono" is the

respectful,

but not subservient form of address, used by Washu for Tenchi and
Cologne for Ranma.

I think sama is correct in this context, certainly more so than dono.
This is because dono is almost purely a literaray word in modern
Japanese, so to use it in speech would be considered archaic.

---
Fabian
Mind the gap