Any place everyone else isn't
In reality, we like to see the MK parades in Frontierland, usually less crowded...as you get closer to the Hub the crowds increase and Main Street starts to look like Bourbon Street on Mardi Gras Day
for Illuminations the "back side" of the WS lagoon is always a better bet as it seems like everyone else is in the WS plaza between FW and WS
for Wishes I have always had the pleasure of seeing the castle straight on from Main Street, so I don't have any suggestions
for the parades in MGM and AK as far from the "main drag" as possible would be my best guess....
hope this helps, im sure others will add their thoughts too