My impression is that 13x13 might be a bit more helpful or accurate too, and the games might not be too much longer than 9x9.
For 9x9, I think it is difficult to lose on 5-6+ stones, even with a large rank difference (though possible for total beginners), and on a side note, I have been wondering whether 9x9 handicaps on OGS are really accurate.
The handicap stones seem to have so much weight on such a small board, and Black seems to receive quite a bit more than what ‘feels’’ even to me.
For example, in all of the 9x9 tournament games I have played in which there has been an auto-handicap, I have found it nearly impossible to win at the handicaps the server gives automatically.
(5d vs 12k meant 4 stones handicap with reverse komi of -5,5 and vs. 19k meant 6 stones.
When I’ve played against a fairly new beginner friend of mine – a 24k – with 7+ stones on 9x9 via OGS auto-handicap, she always won. It was nearly impossible for me so long as something was defended.
Even 2 stones against a 4k on 9x9 is very hard for me, and I have the impression each stone is worth around at least 6 stones of 19x19 handicap, although OGS gives much more handicap to Black on 9x9 than that.)
Searching through the forums, I see an old post about OGS not computing 9x9 handicaps correctly. I wonder whether this is still the case.
Edit : Ah, I found this further down that thread, too :
And this, from the GitHub bug ticket following that post :
That is approximately the same win/loss ratio I have as White in 9x9 handicap games with handicap above 1 also (1:8 or less), so perhaps the OGS 9x9 handicapping system should be looked into and adjusted to be more accurate ? ^^