The Cafe is a sit down style with waiter etc. where the express is a counter service type where you order your food at a register then are given a number and the food is brought to your table...kind of like Pei Wei if you have one by you. I really like the express it uses a counter service credit if on DDP vs. a TS if you go to the Cafe and I find the the express to be amazing!!!
I've never eaten at the cafe but we love WP Express. We make a point of eating there each and every trip we take to Disney. It's CS credits on the DDP that feel & taste like table service. Sitting at the tables outside for dinner is a really great way to relax & wind down after a hectc day at the park. We've been during Easter week a few times now and as busy as everything else was, we've always found ourselves a table there.