I had given up on the (practically abandoned) official Twitter for Mac and switched to Osfoora a few months ago. It's been great but I have some minor issues with it (Space pages down instead of up, lack of keyboard shortcuts for interacting with individual tweets).

I've found Tweetbot to be rather stable for an alpha release, and I think that Tapbot's strategy in releasing this early is to get people to fall in love with the app ASAP so that everyone will raise hell if Twitter takes action against third-party clients.