C-17 and C-141 guy here. The nice thing about the C-17 is jet speeds, jet engines, travel the world, and participate in world events as they happen, like earthquakes, hurricanes, contingencies, evacuations, VIP and Presidential support. For example, I flew into Berlin as the wall was dismantled, Panama invasion, all the wars and skirmishes since 1987. Left 6 years of active duty with 4400 hrs of international heavy jet time, which the airlines love. My buds in Tankers had 1500 hrs total in the same time frame. To be fair that was during the time they sat SAC alert a lot. The nice thing about C-17 is it’s new’ish, you get to taste all missions, Airdrop, tac low level, special ops, Air refueling etc. we had a few Tanker guys transition into my Reserve squadron and they liked the challenge of the mission but complained about all the currency. Either way, if you notice the responses so far, most guys like the plane their flying and enjoy the mission. If your goal is Airlines, I think a KC-46 would be tough to beat nowadays.
Good Luck