Personally, I would get the man what he wants, regardless of what I thought was best.
Secondly, in my personal opinion and experience, a 44mm Swavorksi will be plenty bright for twilight hunting, AND a 56mm scope presents it's own problems in general. The bigger the objective lens, the higher the scope must be mounted, and the higher a scope is mounted, the more "off-bore" issue you have at long ranges.
Thirdly, and most importantly to ME as a shooter, an 18x vs 12x is a BIG difference. If I WANTED a 12x and you got me an 18x, that's one thing, I could probably get over the fact that it's not exactly what I wanted because it's a higher magnification scope. But if I WANT an 18x scope, I'm not going to be satisfied with a 12x scope. Personally, my effective range changes greatly dependent upon magnification. You can't shoot what you can't see.
Fourthly, I have had tracking problems with Zeiss scopes in the past. 10clicks up and 10 clicks down doesn't always end up in the same spot, and that's a problem for me. The two swaroski's I've had have always been spot on trackers.
So at the end of the day, I'd get the guy what he wanted, no matter what. It just so happens that his choice ALSO mates up with the higher magnification AND the better tracking AND the better riding scope...