They're Mike and Joel, or Kirk and Picard. Both good, but in different ways.
I prefer Cavanagh Thawne right now, because he reminded me how much I love it when you can't tell which way he's going to go. When he's on, he's on. In his scenes you can really get a sense for how dispassionate and cruel he is with his hate, but there's also an infinitesimal tinge of genuine compassion for Team Flash, or at least enough disdain that leads to him not feeling the need to overtly destroy them at any time. You can see him constantly weighing the situation and his options and the outcomes.
Every conversation sits on a knife-edge where he can either lash out and suddenly do untold damage, or just calmly hang out with them and berate them because, eh, what the hell does he care? It's great.
Exactly how I feel. Letscher Thawne has no attachment to any of them beyond his outright disdain for Barry as a person, whereas Wellsobard is just enough of a human that he becomes almost totally unpredictable. There's actual chemistry between him and the cast, and all of his interactions with Cait, Cisco and Barry are colored by that.
I love Letscher's take, but I think he fits way better in Legends where he has no connection to any of the primary characters and just shits on them constantly because he's better than they are and he doesn't care.