I get the most power from my fairly big ReactorCraft reactor, which has 32 cores I believe, but I find that I often have no need for that giant amount of power all of the time. I don't leave my bigger power draws on 24/7 because I simply have no reason to plus I'd run out of stuff quickly. I only ever turn on my steam turbines from the reactor when I need to use a ton of power for extractors/grinders/electrolizers/whatnot.
Other than my ReC reactor, I got a fairly standard big reactor covering all the costs of maintaining all the automation and EIO/TE/Mek machines in my base... at a surplus of power too. Yellorium production is automated so this will theoretically never ever shut off unless my automation breaks and I don't notice for the 16k yellorium ingots I have in my ME system. In addition, I have a row of 8 gas turbine from RoC (jet fuel is also automated). I really just built it for the fun of hearing multiple turbines spin up, but this can supply me with enough power to run all of my bigger power draws in the event that I don't want ReC scale of power, but need more than my Big Reactor can give me. I also have some EU furnace generators attempting to use my massive surplus of coal, but I generate coal at much faster rates than I use it.
I also have more eco-friendly ways of obtaining power. Granted I get the least out of these, the benefit of having passive power is too good to pass on in the case that something else fails (which honestly is impossible but I'm way too cautious anyway). I got 5 Mek wind turbines at max elevation generating a pretty decent amount of RF and I got 20 64Rf/t solar panels from SolarFlux in a RFTools dimension that has no weather and is always daytime.
And if that wasn't enough, I plan on creating 2 more reactors for ReactorCraft, one of which will be a fusion reactor.