Is there a Rainforest Cafe anywhere close to where you live? Is it within driving distance? Have you ever visited there before?
If you answer yes... then why go to the one in Disney? To be honest, when I go to Disney, I want to experience something that I cannot get anywhere where I live.
After having been to the Rainforest at DTD in WDW and the one here in Toronto, I can say both were different dinning experiences. Yes both locations were set up the same and the menu was 99% the same, with some items not on there. However there is a huge difference in visting a Rainforest Cafe in WDW and one where you live, if there is one.
I would recommend going to the AK Rainforest for a big breakfast, then grabbing lunch on the go inside the park. None of the other Rainforest's serve breakfast. We usually walk in with no reservation and have the place mostly to ourselves. And (most importantly) the french toast and eggs benedict can't be beat!
Always had a huge wait time to get in RFC, but usually at the DTD location. After a truly pricey lunch there in January, I think we're done with RFC. If you can get on the DDP, I would go for it.
At AK, our fav is the Flame Tree BBQ. That's nature at it's finest...beautiful gardens, incredible birds, views of the animals (sometimes the gorillas are up in the trees)...and best of all .... IT'S ALL REAL!!! Why pay those prices for fake rainstorms, fake animals, etc., when you can experience the real thing for less.