Winner: Dallas Mavericks
Although they were limited heading into the summer, the Dallas Mavericks came away with one of the best free agents available in Klay Thompson. The cost was relatively small too, with them shipping off Josh Green to the Charlotte Hornets in exchange for two second-round picks that they used to send to the Golden State Warriors in a sign and trade for Thompson. Thompson isn't the player that he once was but he can still help the Mavericks.
Had he stayed in Golden State, he probably would have played a sixth-man role but will probably start for the Mavericks and give them a potent offensive weapon to pair with Luka Doncic and Kyrie Irving. He averaged nearly 18 points per game while shooting 38.7% on nine 3-point attempts per game and may play a similar role in Dallas, but hopefully with more consistent production.
Factor in them swapping out Derrick Jones Jr. for Naji Marshall, who is a better shooter and younger, and Tim Hardaway Jr. for a more promising Quentin Grimes and the Mavericks replaced three rotation players with better versions of the players they moved on from. Great start to the offseason for the Mavericks.