Early to Mid Game - Ender IO's Advanced Photovoltaic Cells in the Eden dimension with a tesseract. They don't work in the End dimension, BTW. Later on down the line, I hear that the dream world dimension is eternal day as well.
Late game - Netherstar Generators (later game) give 40,000 RF/t
For the reactors, on a server, I made a 17x17x3 reactor (or so - forget the exact dimensions) that gave 42,000 RF/t. This pretty much used up all of my early game resources. I never use the x64 generators - they use up too much fuel too quickly.
Magmatic Dynamos gives 80RF/t (pyrotheum lasts a lot longer, too). These are usually my early go-to power option.