170-180 cm. it really also depends on the guy height... but for me a 170-80 would be great. I'm 187 cm. and bra size well just normal size as long as they're good looking I guess. size matters though but a normal size it's just fine. But there are also other attractive things on a women all its not about the breasts. unless you're flat ( I'm talking about totally flat) I wouldn't recommend you to get them enhanced or things like that. I personally don't like that at all. I'm not saying I don't like breasts. I think every man likes that. anyone who doesn't it's just lying to you trust me. But that doesn't you can't be hot. there's things more important for me. like the booty. A bit of workout wouldn't hurt time to time to get it bigger. a well foemed booty would please a me more than having huge boobs and no butt. that's just my thoughts though... :)
If you SERIOUSLY wanna know my perfect bra size without getting offended, it'd be 32F, though I wouldn't expect every chick I find attractive to have balloons attached to her chest or anything, hell anything above AA and I'm ready to rock.