Very often a patient will come to the office with a cane already in hand. It's usually second hand, often ancient and almost always way too big and held in the wrong hand. I've been taught by physios about cane use but only lately did I look up some of the literature. There is evidence that canes significantly decrease the forces subjected to the involved limb, by up to 35%. The ipsilateral/contralateral question seems to have been largely resolved as well. Several studies have demonstrated better results using the cane in the hand opposite to the affected limb. I did find a single study that suggested that ipsilateral use might be preferred for medial knee osteoarthritis alone, because cane use transfers forces medially. The length of the cane should be measured from the floor to the crease of the wrist, or for the mathematically inclined;Height X .45 Metres+.87M. I couldn't really find anything about handle selection. The Mayo Clinic says to go with anything that feels comfortable but the physios I have worked with are all against the traditional curved handle and favour the flat handle with offset. The above mentioned Mayo information site has a nice little slide presentation for patients to help select a cane.
One more point. Often overlooked is the handiness of a cane in the case of invasion by aliens with large metal heads.
But don't even think of trying to handle them without warming up.