Replies so far have noted several factors to consider. As always it begins with your
local situation. In my situation--semi-arid, high elevation--I'm not so concerned about maximizing sunlight. Light is intense here and there are few cloudy days. Moisture is at a premium though, so I orient my beds across contours to slow the flow of water down the slope. Elliot Coleman also indicates that a slope of a few degrees to the south will capture more
solar rays and raise temp.s a couple of degrees. My observations seem to confirm that and since I'm looking to extend my 100 day growing season significantly, I try to build beds so that the top surface has a southward slope. Fortunately the larger scale slope allows me to orient beds generally E-W to easily allow for a southward sloping bed tops. In my annual market garden I do grow taller stuff on the N half of E-W oriented beds and shorter stuff on the S half. I don't mind the taller stuff shading the paths between my beds at mid-day. In fact I like to take it a step further and
mulch my paths with lots of
wood chips to maximise the absorption of water and minimize evaporation.
In my winter beds--under a hoophouse or low tunnel--I grow greens randomly, broadcasting a mix of
seed. The plants seem to naturally grow in clumps. The air temperature at ground level within those clumps is higher than in the more barren areas (it's all mulched fairly heavily) in between them. Even in this relatively moderate winter, we've had single digit lows regularly. These greens wouldn't have survived the temperatures without several layers of agribon--enough to reduce the block 50-80% of the sunlight according to the manufacturer's ratings--and one of plastic. Early on I removed the agribon regularly on sunny days in order to maximise the sunlight. More recently I've found that the plants did just as well being covered all the time. I've concluded that their growth is going to be slow regardless and that temperature is more of a limiting factor than sunlight.
I have some further reservations about orienting plantings/bed in order to maximise sunlight, at least outside of areas where sunlight, rather than moisture or warmth is at a premium. The amount of
solar radiation striking the earth over the course of a day follows a bell curve, with the maximum intensity in the middle of the day and the proportion of
energy building up and tailing off sharply. If I was more concerned about maximizing sunlight, I'd want to find out more about how much plants depend on the intense mid-day sun versus perhaps how little they can get from the relatively weak morning and evening sun. Perhaps it only makes sense to maximise for mid-day sun as working to get more early and late day sun can't really net you much more solar radiation? Another dimension to my reservations is that forests and grasslands everywhere seem to get enough sunlight without worrying about bed orientation. And for all its faults, conventional ag--both pre and post industrialization--seems to have enough sunlight to grow crops without growing in raised beds oriented in any particular direction.
