If you do a search here for "oil cooler", you will find more than you ever wanted to know
The braided AN lines are usually viewed as the "best" due to their strength and heat-resistance (and good looks too), but are not cheap. You can easily spend a few $hundred just on the hose and AN fittings.
Most guys use either -10, -12, or -16 sizes depending on the specific application (engine type/size and driving conditions.)
The non stainless-sheathed oil lines (usually blue) are another option, but personally I would be reluctant to use hose-barb type fittings if it were my engine at stake. Spring for the good socket-style threaded AN stuff.