Coming strait form a reactor, do nuclear reactors produce the biggest amount of energy that we can manipulate?

You mean, "straight from"? What is "biggest"? Its meaning is relative.

Yes, the straightest form of energy. Or is there something bigger we could manipulate?

Hm... nuclear reactions are highly controlled so that they don't release too much power at a time. Too much energy cannot be manipulated. This is why nuclear plants have strict measures to ensure the safety of every worker and the people closest to the plant.

Up to now, I would say yes, nuclear energy is the form of energy that contains the most amount of energy known to science.

Per unit yes with regards to present day possibles

Not necessarily, anti-matter produces energy with 99% efficiency while nuclear reactions only have about 1% efficiency. But sadly, we don't have the capabilities to produce large amounts of anti matter, as less than what would fit on a needle-tip has been produced through the use of particle colliders. Also, hydrogen fusion is very efficient, but I don't remember the specifics of that.

Hydrogen fusion could be the future of green energy if we can make the process last for more than 10 seconds.