They are very different restaurants with very different menus. You should check them out - they are posted here on the Dis and on allears.net We like Spoodles better than Big River but if you just want a burger or sandwich or have picky eaters, Big River might be a better choice. Or if you are a beer fan.
The hubby and I just tried Spoodles for the first time a few weeks ago and it was terrific! We shared a couple of appetizers and then had dessert and it was all very tasty - and I'm a pretty picky eater.
We haven't eaten at Big River in a few years - we just weren't that impressed with it, although their beer was pretty good.
We've done both. We would go with Spoodles over BRG any day. In a couple of visits to BRG we got consistently poor service and food. Enough to make us not willing to try it again. There are just too many other good places at WDW to eat.