Earth in the near future (in 2081) is invaded by aliens who are just "a bit" more technologically advanced than humans. The war is not a one sided extermination of humans, but humans are about to lose anyway.
An engineer succeeds in building a time machine for a one way trip to the past. From How fast could a civilization advance if given access to information from future? I understand that there would be many problems, but this is the only option nonetheless.
He is one of the last surviving humans and he alone must depart as soon as possible.
There is some space in the time machine for luggage (think DeLorean from Back to the Future -
it could be a bit bigger if need be, but not larger than a small truck) and the engineer takes a tablet with all human knowledge and an advanced AI that can function as a military, economic, medical, ... advisor (so the question is not about what knowledge he should bring, but to whom he should bring it), a Google Glass like device that can translate all ancient languages, a small fusion reactor - but then has to decide what else to bring with him (for example: penicillin mold, genetically modified seeds, ...). between bringing either:
- the latest computer with as many spare parts as can fit in the time machine (but eventually the spare parts will run out and you have limited number of computers in the world)
- all the tools (and tools to make tools) to start mass producing an 1955 era vacuum tube computers for the whole world (but this progress will be much slower)
What is the best option and how far back should he travel to benefit most from the technology of the time (so he can build on the existing infrastructure and knowledge of metallurgy, medicine, science, ... of the time and perhaps influence a great historical figure), but still advance the human civilization the most? 2000 AD? 1500 AD? 1000 AD? 500AD? 500 BC? 1000 BC? 1500 BC? 2000 BC?
EDIT for "put on hold as too broad":
Thank you for so many great and interesting answers!
I see now that the question really is too broad and I have modified it in a way that hopefully leaves the existing answers still relevant, while being more specific. If the question is still too broad, I can narrow it further.
What I removed from the question is in
strikethrough and what I added is in italic.
TL;DR: One of the last surviving humans must travel to the past to give the humanity a technological head start in the battle against invading aliens. His computer contains an advanced AI adviser with all human knowledge and the question is: to whom should he bring it to maximize the chances of success, considering that traveling further back in time increases the possible technological advances, but also the uncertainty of success?