Yet another person overlooks oil entirely. This must be a lasting side-effect from the days when oil sucked ass generally; the buff to its power output per bucket is actually quite recent.
No, no, don't get me wrong, I love oil. Currently running my base on fuel in boilers. But it's not really a new-guy friendly power source, and it's really more useful for MJ than EU generation.
I'll admit the diesel generator is an interesting idea, and not ridiculously expensive, but it's power output is lackluster. Running the fuel in combustion engines is a decent way to go, but then you have to deal with conversion of MJ to EU (as well as with cooling down the combustion engines) which adds extra steps and danger.
The assumption here is that this is OP's very early power generation so anything that requires a high degree of complexity or multiple machines to build isn't really useful for him right now. The neat thing about geothermals is that you can skip generators entirely and go right for geothermals.