It all depends on what each person considers to be worse.
If we talk only about who has disrespected the sport more, the obvious answer is probably Tomic. He has shown a lack of passion and dedication pretty much his entire career (except for a brief period in early 2016), he tanks matches and is only here for the money. Personally, I find his motives to stay a little more respectable and less superficial than those of Nick (to be famous
), but at least Nick tries harder and is less cynical in his approach.
Now, if we talk about who disrespects people more, Nick is that guy. With Tomic you know what you are gonna get, with Nick however there are times when he plays really well, he has a couple of brilliant matches and makes all of us believe he's on the right path and then, in the middle of his new found focus, he tanks and that pisses many people off, especially those who bought tickets. There is also his incident with Stan in the locker room, a obvious product of his horrible comments on Vekic (I'm still trying to understand what the hell he was thinking about while saying it), and his multiple tantrums on court, in which he unleashes his frustration against umpires, crowd and even ball boys/girls.
Both are ugly representatives of this sport, but my vote goes with Kyrgios. Many people tend to be more lenient with him just because his game is more 'entertaining', but the impact he has had is bigger and the image he gives to the sport is worse than what Tomic has done.