I prefer the space as thousand separator, personally. 1 000 000. And I think that if you're going to use both periods and commas in numbers, then you should use the period for thousand separators and comma for the decimal separator. 100.000.000,000.000.001 looks more logical and balanced to me than 100,000,000.000,000,001. Not that it really matters anyway, it's mostly aesthetic preference; but I find it easier to instantly see where the comma is in a sea of dots than to find the period in a swarm of commas.