Yeah, I think there are basically three good spots.
Want no dragons? Warn the Jarl, but upon being told to go get the Dragonstone for the nice (or, more bluntly, sarcastic) wizard, tell him politely you'll get on right on that and go off to do whatever else you want to do in the world. That should be no dragons... I think, and while it makes sense to give the news to the Jarl straight away, you don't owe him anything else. (The problem is you often have that stone from doing the Claw quest beforehand, and you can't drop/stash a quest object, so you'll have to sort of tab out of that conversation or just never go and chat about it with said wizard.)
Want some dragons? Go up to get your training from the Greybeards, but wander around rather then going straight to the horn. It is, as I noted before, pretty far from the mountain- if you were like me and rushed the main quest, that's a long way to walk. Getting distracted at the various towns and stuff around as you sorta head 'in that general direction' seems sensible.
Want even more dragons? I believe you get more spawns if you do 'wait' while the invitation is being gotten for you, and indeed that's a reasonable time to stop- you're waiting on anothers work.
I think I may have discovered another place that could make a decent stopping point, but those seem pretty good.
