Probably go Jaylen. Smart is just a little too short, although he would be my second choice. Tatum isn't strong enough. Semi is a valid option but Giannis would be playing 40+ so one of the regulars would get most the minutes.
Real answer is probably its a team effort.
Yeah, I go Jaylen. His strength lies in on-ball defense and he has the size and determination to at least make Giannis work hard. Also, on offense, he is likely to be a little more off-ball than Tatum so he should be able to focus more on his defensive assignment. Fwiw, I actually think Tatum has been a better overall defender this season; but that's mostly because his team defense is at an elite level.
Guys like Smart, Semi, and, of course, Tatum should work well in spurts, but I think the guy getting the most consistent time against Giannis should be Jaylen.