i remember this one time...
it was new years 2003 and we were in EPCOT, Illuminations had special times that night, for obvious reasons, and we stood in between Canada and the UK. At midnight we stood and watched the best fireworks display, it was probaly twice as long as the normal Illuminations. It was one of the most spectacular moments i can remember from WDW vacations, even though i have been there nine times (but whos counting?) in 17 years.
Anyway to answer your question, anywhere is a great place to watch it but i would say canada and UK area. Also it doesn't so much matter where you sit, but who is around you and if you get there early enough so your not behind any tall or fat people.
Another tip, don't try to position yourself by sneaking in front of people, they get angry, trust me I witnessed an old man yell at this young mother trying to move her children so they could see.