I use Twitter a lot, but that doesn't mean I wouldn't jump at the first chance of a real alternative.
The number of sponsored ads don't seem high enough to make me feel like it's annoying.
As for Twitter clients. Eh, not sure I care so much. I just need a decent client which doesn't suck.
I think their recent decision sort of suck but as a user I don't know that I care too much.
They just joined Twitter, years after it was launched, because they wanted to see what interesting people & celebs were saying. Heck, the probably even heard about Twitter from an advert or some sort of marketing material, so adverts within Twitter won't bother them/me.
Communication should be controlled by the users. Think about all the companies who were screwed over by Facebook's "Likegate." Decentralization is why I prefer Tent and IRC. App.net seems acceptable as well because of the open nature, though it is centralized.