I really like W:MoD's thief Wario outfit and I wish it was seen more. I just like the design a lot. But I guess my favorite would be classic because of Wario Land.
Really can't go wrong with Wario's classic getup, but I'll admit I have a huge fondness for the Ware biker outfit and how it makes Wario more distinctive from Mario, while also really fitting his bad boy persona. I really wish more Mario media would include it as an alt.
I've always been more of a Warioware fan than a Wario Land fan but I love the biker fit for Wario. I know this is purely headcanon but I've always seen it as Wario seperating himself from Mario's image out of spite. Becoming something of his own and discarding anything even resembling the guy. Shoutout to his golfing outfit. He had that shit on.