How much to put to down to get the BEST returns?

[Tom Smith]

How much to put to down to get the BEST returns?

Should you always put in 20% down, or is there another percentage to put down to get the best returns? 

Let's use an example:

$80k purchase, $1,200 rent/month. Total interest would come out to $56k over 30 years. Is it better to buy this condo/house all in cash, better to finance with 20% down, or finance at another percentage? 

Would it ALWAYS be best to finance with just 20% down? Does it depend on how much money you have? Let's say you have 1 million dollars and are buying a $80k purchase, should you still only put 20% down or should you just buy the whole property with cash?