Awww Milt, the boy asked a straight question!
I can't remember exactly, but propellers with rounded tips are less draggy and more efficient, but props with squared off tips have higher solidity and so you can stuff more power through them e.g. for short field aircraft.
I'm sure that someone can give you a more authoritative answer before long, but if you simply can't wait try searching on 'hercules' 'orion' etc.
Jeez, the things people think about at xmas
Happy New year,
N