The three main locations to view fireworks are from the Main Street/Hub area, It A Small World Mall, and the Rivers of America.
It's a Small World Mall is fairly popular, but I don't think any of it really designated for sitting (maybe up on the raised area on the right side some guests might sit on the benches/planters). The projections are on the facade of IaSW, so you'll need to be able to see the building. I watched from fairly close to IaSW and the view was okay, but the toy shop did get in the way occasionally. I'm not sure if it's better to be close to IaSW or closer to FL. Hopefully other will chime in. Another thing to note; this location is closer to where the fireworks are launched, so the bursts are noticeable louder.
The other location is the Rivers of America. The use the mist screens for the projections. Make sure you're viewing the show from more towards the NOS-side of the river. Basically you want to be able to see the River, plus Big Thunder if you don't want to have to split your attention. These photos are taken from the NOS-side of the RoA, in line with about Cafe Orleans.