Trump - Just good allround and does well explaining choices etc. Clam and collected, positive etc.
Firebat - Great to watch, can play a wide variety of decks really good. Does well explaining choices, is critical etc.
Zalae - Can be a bit irritating at times to watch because he puts a bit of a macho attitude on, which to me is grating. Excellent player though.
Thijs - Generally positive, can play certain decks really well (he's poor at Hunter or anything mildly agressive) ... does have irritating moments though.
Dane - Awesome, funny, positive Wild player ... always trying out new things.
There are a number who are decent ... Savj, Kibler etc. but I can't watch them for longer than a game because they are clicking all over the place and are really jittery and nervous. I can't stand how Kibler constantly looks to chat etc.
I generally don't like watching players who check Twitch chat more than actually playing the game and so making massive misplays because of it (e.g. RegisKilbin).
I would suggest watching a number of their YouTube videos ... Trump has good long videos for Arena, Firebat has daily content (short videos) that's fun to watch. There in-depth stuff with Omni/ etc. etc. etc.
Isn't that kind of the point of streaming? The interaction between the streamer and the viewers is exactly what makes watching streams fun imo.
I mainly watch kripp for entertainment but he is certainly very good at the game so I've also learned a lot from watching him. If you purely want to focus on improving though I suggest you check out Zalae and Firebat. I watch most of their videos on omnislash and they are very good at explaining their thought processes in each turn (why should I play this and not this?) and they also focus a lot on deckbuilding in their omnislash videos which is very interesting as well.