Thank you all for your great feedback and input.
After reviewing and testing orders in both Paypal and 2CO, I've decided to go with Paypal. It really came down to user experience, and I find Paypal's interface to be a lot cleaner and allows our branding to stand out.
I tested 2CO's one-page checkout, which is great, but their branding seems to take over the page. It's a bit too overwhelming and our branding is easily overlooked, so our customers may wonder if they're on the correct page.
I will hand it to 2CO, however, for their excellent and highly responsive customer service (which Paypal needs to learn from).