I've had great luck getting TS reservations by trying for ADRs as soon as the booking window opens. If you've never been, then I highly recommend inside for the full experience! It's so much fun, more so if the other people around you are likewise having a good time.
The outdoor area is nice for larger groups or if you're not interested in all of the interactive stuff inside. It has a more laid-back Polynesian vibe, and often there is a band that plays beautiful island music as a nice background. Menu and drinks are the same.
You can also order drinks from the outdoor bar.
I love both inside and outside seating, but I would really encourage you to try inside if you've never been!