Not this Star Wars fan.

: The question I'm posing to you guys is this: If the Halo universe were real,
: and you could live or work there, where would you want to be?

Not a Spartan, supersoldier, or ONI agent. They're fun to watch, not fun to be.
Don't want to be a scientist. Red shirts aren't very flattering on me.

Honestly, I don't think I'd want to be a part of the UNSC at all. Ideally, I'd be a free citizen kicking around on Venezia, working in construction or the nascent manufacturing industry. Perhaps there'll even be a way for me to work on ships or aircraft.

And once Covenant refugees start showing up, I get to putter around in Ghosts!

: Personally, I would want to be a part of Infinity Science. Getting to travel
: to various alien worlds,

And blow them up/crash them into suns/crater them with impunity.

: work around the most advanced tech humanity has to offer,

Stolen technology. = )

: (and maybe any other Covenant that end up onboard).

So, you'd be an interrogator?

: Field studies would be a blast, as well as any work
: done in the lab.

Don't go into the field. You'll just become a mystery for any Spartan IVs sent to investigate your radio silence.
And the lab... well, stay away from Forerunner artefacts, and you should do fine. Just in case, it would probably be a good idea to learn Sangheili.