This should be a no brainer. I'm kinda shocked how #2 and #3 got votes. I bet my arguments have already been stated, but since I missed few days worth of posts I'm not gonna go through every thread 100%.
#2 is aboslutely terrible as an option as after you get "the guy", you need to start building up, not tearing things further down. First off, if you get Flagg and trade Lauri you are trading away a guy who is the type of guy you are then looking to acquire 2 years later and may not be able to. It would also be better to have the rest of the team in place BEFORE you get the guy, so that others being less developed than him arent dragging him down. The time to "wait for maybe getting more kids who may or may not turn into players" kinda ends the exact moment you draft HIM.
#2 is sensible ONLY if you think that Flagg isnt the guy, and you are looking to get the guy next year (Good luck with that two #1 picks in a row thing!).
Also #3 AKA getting yourself in contract/tax trouble way before that guy develops/peaks is also definitely not a good idea.
#2 makes sense if you think that Flagg's peak timeline won't matchup with Lauri's peak timeline, and you want to get assets from Lauri that will help you surround Flagg with talent more in line with when you expect him to be at his peak.
#3 makes sense if you are impatient and are sick of the Jazz losing games
#1 is a huge risk as you might be setting yourself up to be giving up pick 9-14 to OKC vs not having to give them anything.
(I voted for #1 BTW, but I don't think it's a no-brainer)