The glasses should match the bottles
I agree with Steve Hosgood: 50 cl and 33 cl sound about right to me - and they're both not coincidentally the same size as beer bottles. Both half a pint (284 ml) or 250 ml are just too small to bother with for everyday drinking (yes, even for most girls I know), although I can see the use for 'taster' measures. As for the extra 68 ml (mouthful) in a pint? Well, that's the warm beer at the bottom of the glass that I'd rather not have to be paying for anyway!