Never trained a 141 guy but flew with them obviously. I would venture they would be similar to 17 guys. I have only worked with one C-5 guy and he was pretty decent, but flew GA for fun, so that discounts it. C-130 guys usually do pretty well for some reason. I am guessing they do more stick and rudder flying. My cousin went from a 130 to a Galaxy and he said the C-5 is boring. I am guessing that substantiates it. No idea why one would be better at multi-tasking than the other though.
Of course, the best are generally fighter guys. It has a lot less to do with stick and rudder than multi-tasking. Lets' face it, a Seminole is not a hard plane to fly. The big part is being able to Fly the airplane, talk on the radios, set-up the approaches, set-up the GPS, etc....All things two people do in big planes. Fighter guys generally do all that every day, and shoot at each other.
In the T-37 and T-6 pit programs, the -135 and -17 guys generally do not do as well as the fighter guys... but according to the PIT IP's I flew with that was generally true of all heavy guys versus all fighter guys, not really specific to those airframes versus any others. The reasons are pretty obvious:
1) The T-6 or the T-37 is basically single seat, and anyone coming from a heavy is used to a division of duties and running a crew.
2) The trainers have no autopilot or automation, and one of the skills of learning to fly large airplanes is learning to manage the automation... but of course that means that you don't hand fly as much.
3) The lighter airplanes react a whole lot faster... that takes a little getting used to, just like going from a small airplane to a large airplane takes some getting used to because they react a lot slower.
4) Heavy drivers of any stripe do not fly close formation, but a big part of T-37/T-6 is formation flying.
5) Mentality is different when it comes to emergencies... in all heavies, there are very few emergencies that require immediate action, and in most cases, after you handle the immediate actions you are still going to be airborne for a good hour or two before you can land... In a T-6, especially (less so a Tweet), quite a few of the emergencies require you to basically be turning toward the nearest airfield within about 3-6 seconds of recognizing the problem or you wind up giving the airplane back to the tax-payers. Also in most heavies, you see a problem, handle the memorized "critical procedures" (i.e. boldface), and then break out the books and read about the rest of the issues. In small trainers, as in fighters, you don't have room to carry the books on board, or someone to read them to you even if you did. So everything is memorized.
In the case of the C-17, there is another potential difficulty to overcome: the C-17 auto-trims. Basically, you set the pitch and hold it and the computer trims it off all by itself. I heard from an F-16 driver that the -16 does the same thing (but of course the -16 is a lot closer to a T-6 than a C-17 is... not that it's really that close either, but still).
Fighter guys tend to similarly sink to the bottom of the class going the other way, i.e. transitioning to a heavy (at least according to some of the guys I know who teach at Altus). It's basically the same issue: unfamiliarity with a new type of flying, different pace, different skill sets, etc. In both cases though, the difference doesn't seem to last very long. I know quite a few heavy guys who became great T-6 IP's, and the few former pointy-nose types I know who transitioned to heavies have all done great as well past those first few months of getting used to things.
Actually reminds me of a story. About 10 years ago, I flew with a KC-135 IP who used to work out at Edwards. This IP was out there doing test flights on -135 upgrades, probably about 10 years before she told me the story (about 20 years ago, if you're keeping count), and talked about when Chuck Yeager used to come out to the base and fly. They would let him fly pretty much anything, based on the fact that he was Chuck Yeager. Of course, he had to fly with an IP, because he wasn't qualified in the airplanes. She said she had never been more scared in her life than when Chuck Yeager was at the controls of a -135. He basically tried to fly it like a fighter and would have put the gear through the wings if she hadn't sent him around... about 10 times.