I tell them my KGS rank since it's probably the most accurate (small sample size over-the-board, OGS/DGS have problems with ranks lagging behind your strength if you're improving, and I don't use IGS...) I do add 'KGS' after my rank though for clarity when people ask .

My KGS is 8, but i know thats inflated from not playing enough on there. My OGS rank is 32, but I feel that may not be right either... My DGS rank hovers between 15 and 17, and altho that is where I play the most, I think DGS ranks are a little low too. So if asked I say around 14 or so, but in my case it doesn't matter much, since the whole idea of playing online is that it should self-equalize, so I just play whatever my rank says I should.

I always use my national (AGA) rank,

I could use KGS, but I have a very strong tendency to play at 3:30 in the morning when I've got several other things on my mind. The rating may be correct, but in a "Broken clock is right twice a day"-kind've way.

Personally, I don't see a bias toward a higher number rank. (I always suspect that folks who announce their rank in the rating system with the lowest numbers think everyone else is overrating themselves.)

The AGA rating is the one I've worked the hardest on, and contains some of the games I'm most proud of. So I use that one.

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Tactics yes, Tact no...

I use KGS-1