I've always listed in USD on .com but since sales have been really slow lately, I listed my last set of listings on .ca in CAD. So far I've sold just 1 of 10 listings to a US buyer. Mind you, this was a Buy it Now which was purchased Dec. 12th and I still haven't been paid. Hopefully it's not because the buyer just realized it wasn't USD that he was bidding. Could never understand why buyers would Buy it Now and figure that they could Pay it Later!
I guess before answering which currency is better I'll have to list a few times in CAD.