There are too many great games that were on the Amiga to even name a top 10, let alone best ever. Turrican II, SOTB, are great possibilities, but jeez... How many other classics did Amiga have?
You guys all missed :
WORMS
Indianapolis 500 (best racing sim, and catapulted Papyrus out of obscurity)
Microprose F1GP (which still has leagues today!)
Populus
Settlers (die Siedler for Germans)
Another World
Flashback
.... and the list can go on and on....