I've personally been to the medical research department and I've also spent time doing the technology research.

I think both are valuable for different reasons. For obvious reasons, I think one more will be more useful to you than the other. They have a lot of updated knowledge there, but I've found that the people I've seen there are pretty open minded about learning how things are done in other worlds.

If nothing else, I'd recommend using the visit there to pick peoples' brains and get as much information as possible at once. I mean, it's not like they'll forbid you from returning even if you don't make it permanent.