Not that it affects what we should, should not, or want to, be doing in sessions, a couple of years ago I did some number crunching on this topic a couple of years ago. It was specifically in relation to some Lake District manuscripts (Barnes, Lishman, Betham, Harrison, Wilson, Stables, and Browne) from the latter 18th C and early 19th C.
It involves quite a good number of tunes overall. All pre-date free reed instruments.
D - 44%
G - 34.5%
A -   5.5%
C -   5.4%
F -   2.5%
Em - 2.5%
Bb - 2.3%
Am - 1.1%
Ador- 0.8%
Bm - 0.4%
Eb - 0.1%
Dm - 0.1%
Ddor- 0.1%
Dmix- 0.1%

There were some differences between the MSS, Betham for example was 44.8% in G and 41% in D, etc.