You talking about handles to make lifting easier? You operate in salt or fresh water. You picky about asthetics or you use your boat, don't just look at it? If handles for lifting, how many folks will be lifting?
If your answers are such that it doesn't really matter. Go to the hardware store and buy handles used for opening garage doors. They are about 6" long with about a 1 1/2" diameter gripping section which is wide enough and round enough for easy gripping. 4 holes make for sturdy mounting. Get suitable length fasteners with bolts/screws to fit the holes with flat and lock washers, and nuts. If in salt water get SS hardware which hardware stores carry in addition to Zinc plated steel which would do for most applications and a cheaper price.
Mount just under the gunwale (top edge of the sides of the hull) wherever is convenient for your application.