As for myself it really depends on the mods they are installed.
No RP and no Forestry => :Solar Panel: for endless supply (would it be arrays or not)
RP => :Generator: (harvesting trees => :Electric Furnace: for charcoal)
Forestry => Bees => Free lava => :Geothermal Generator: => profit ?
With EE2+compact solar, it's definitively solar arrays as I get the "god" state really fast.