Generally I would say, overhead is going to give the least shadow problems.
HOWEVER .... there are a lot of factors that can prove that generality, right or wrong ...
* distance from light to table
* expanse of light ... how long, 8ft tubes or 2 ft bulbs? etc ... how many tubes wide...
* # of lightbulbs and wattage
* open bulbs or shades (type/style)
Also, in choosing ideal lighting ... daylight bulbs are going to give you a clearer cleaner light, than the warm or cool bulbs.
Then the dilemma of which type of bulb ... incandescent, fluorescent, compact fluorescent, halogen, LED.
I don't have the answer, but my latest researching and minimal experience with LED is getting me more keen on those, where and when possible.
As an added note ... many light fixtures and lamps say they are for one type of bulb (traditional or halogen or LED. However, many times you can buy the other bulbs (providing they fit) in the other style of light.