Like you, I will commute on any of my bikes even though the Moulton sees the bulk of my city riding as it is just that good of an all rounder.

For trips where I need to lock up and leave I take my newer '76 Peugeot fixed gear (you have to have a beater / bar bike) but most times I have really good bike parking so don't worry about what I am riding from a theft standpoint.

Of late I have been riding a different bike nearly every day as they come out of winter storage... will take me a while to get through them all.