I was wondering about the best, most efficient power source that exist in the whole direwolf20 1.10.2 modpack. It does not matter how expensive it is, but what the best power source is.
For infinite power, near infinite expansion capabilities and relatively low level tech, I've used a Forestry mod tree farm in conjunction with a Railcraft steam boiler/steam engine configuration. Downsides include massive space requirements, but once you have a designated site the system can be easily upgraded with more boilers and a second tree farm if and when necessary.
Have the tree farm up and running, use piping to get the saplings back to the machine and separate the junk to somewhere else(if you're using trees that have fruit, this is an infinite food source as well), direct the wood to furnaces, and charcoal from the furnaces to a storage space between the furnace and the boiler. A 3*3 boiler will take A LOT of charcoal to get heated up, but once it gets to the maximum temperature, the consumption of coal plummets down. It's been a while since I've done this, but a full iron chest of charcoal probably isn't enough to fully warm up a single Boiler. Once it is at the optimal temperature, you can run three or four boilers off a single farm.
As long as the piping filters all items to their correct storage spaces and there's water to the boilers, this setup will provide infinite energy with no hands-on required.
From Thaumcraft, you can also look into some golem based solutions, though I'm not convinced the energy output will compete with the aforementioned steam boiler one.
This setup (one tree farm and 4 boilers) is/was sufficient to run a fully automated base that harvests materials off three different Mystcraft worlds with quarries that transmit all the materials back and that has a a fully automated crafting/ordering system via Applied Energetics and Industrycraft. It wasn't a Direwolf20 world, I believe we were running Techworld at the time, but the relevant mods are all the same.
Another, arguably more novel approach is to use bees. There are bees that produce oil. You can further refine the oil to gasoline and burn that for energy. Producing new strains of bees takes a long time and it took me roughly three weeks of active playing to acquire the correct bee lineages, but it's a fun one. You can further refine the bee lineages to ignore sunlight and flowers entirely, so this solution can be installed to wherever your base is. The initial workload is huge as you need to find several different bees to start the breeding, but as you get a few of the critical lineages purified and a stable supply of their workers, you can pretty much change any queen to any other strand within hours. This system is also much faster if you have the machines for genetic manipulation and you can simply extract the specific traits from the bees you wish to have on your super-bees.
The bee method also requires quite a large space to function, as you need to have a large supply of apiaries(20+ single block apiaries), then machinery to extract the oil, container for the oil, a refinery to turn the oil to gas, another container for the gas, and the generators themselves. But again, once the machinery is operational, the system is fully automatic.
I didn't see the boilers or turbines needed to use the railcraft steam power gen option in the DW20 1.10 pack. Either they aren't in yet, or aren't coming over at all.
What I did for early power gen is ender io stirling generators and some actually additions coal generators. When I had the resources, I started up an ender io farming station for wood coupled with a rftools crafter to make cheap wooden axes feed back into it, Direwolf20 started out his current let's play series with a similar setup for tree farming.
I fed the wood from the tree farm into two actually additions double furnaces to turn into renewable charcoal, and fed those back into the stirling generators. Once I could start affording capacitor upgrades, I switched over to only ender io stirling generators, and built them up to 16 with octadic capacitors each putting out 80 rf/t.
That gave me enough infrastructure and resources to buid a 7x7x7 (chamber size) extreme reactor that produces about 11K rf/t on its most efficient settings, and have it set up to kick on if I start running out of power.
Whatever you decide to do with power, keep in mind when you get in the tens of thousands of rf/t, you're going to run into issues with power transmission and storage with just ender io conduits that max out at 20,480 rf/t and vibrant capacitors that each only hold 25 mil, but can be built up into multiblock capacitor banks. If you want to get into the ridiculous power options you can start into draconic evolution, but you'll have a tough time getting enough draconium to get very far into it, and you'll be sinking millions of rf into the neat stuff you can build with DE at that point as well.