Fusion are the best, but you have to 'light it off' to get it going in a self-sustaining reaction.
CRCS stands for 'Continuously Re-applied Coolant System'. It is a method by which you swap out cooling cells for fresh ones, cool down the expended ones, then cycle them back through. It requires multiple reactors to run, with a complex and convoluted automated piping/tubing system, but you can get EU output in excess of 2k EU/t off of quad-uranium cells. Over 5k EU/t out of plutonium, although it requires a LOT of coolant towers to manage that effectively.
The 'gold standard' for a Mk. I reactor (fire and forget until it needs refuling) is called 'The Beast'. It produces 420 EU/t consistently out of quad-uranium cells.
Head on over to the IC2 nuclear engineering forum, and you'll find a thread that has a list of good reactors. Just... avoid the hybrid reactors for now... they don't really work all that good, and they got a major nerf.
Thermal banks are a very good way to generate lots of power. Here's how you do it:
1) You have a Pump with a Magmatic Engine (Invar is 2x Iron Dust + 1x Ferrus Dust, then cooked up). Lava passes into the magmatic engine and into a Liquid Tesseract
2) The other side of this liquid tesseract is an enormous tank, either Xycraft or Iron Tank from Railcraft. This needs to be a maximum size tank. This is your 'reserve tank', and if you see it start dropping, it means you need to check your lava supply.
3) Use Liquiducts from Thermal Expansion to pipe lava out of the reserve tank and into your thermal generators. You can have quite a few on a single line, since the liquiducts have more throughput than golden waterproof pipes.
If that doesn't suit your tastes, try Boilers
From Railcraft, a Boiler needs fuel and water. Use an Aqueous Accumulator and put a couple of water source blocks next to it, set and forget, to make sure the boiler never runs out of water.
Now you need to decide what kind of fuel to run on. You have several options, but I'd strongly suggest running it on renewable Biofuel if you don't have anyone willing to breed up Distilled Bees.
Boilers produce Steam. You can hook up a Steam Turbine to produce EU, although it eats through Iron at a pretty decent clip. Or you can just run everything off of MJ.