Like the others, I can only comment on the places we stand for these parades/fireworks as there are plenty of great viewing spots really.
Illuminations - as long as the wind isn't blowing in your face (as otherwise your view will be obscured by the smoke) and you haven't got overhanging trees or one of the islands in the way of where the globe sits, you're good. We normally choose either Canada or Norway when we watch.
Fantasmic - we don't do the dinner package because I don't like being in the end sections of the arena, so it means to get our choice of seats we have to get there early. Our personal preference is as near to the centre sections as possible and about halfway up, but we've had great views from various locations.
Spectromagic / ELP - we choose to stand somewhere in Liberty Square, not because the views are any better, but it's usually less jammed than on Main Street. And also we've probably just come out of Liberty Tree Tavern and are too full to walk any great distance!