My perfect Twitter client

I don't want much in a Twitter client. Here it is:

• One tap/click to move from viewing my mentions to viewing my favourite list.
• Highlighting when there are new items from a list, new mentions, new direct messages, etc
  
• Accurate conversation view
• Auto-completion of usernames and hashtags
• "Post using this hashtag" function
• URL shortening.
• Easy image attachment.

On the iPhone, the free Echofon app handles all of this easily and without fuss. I keep trying alternative clients, but I always come back.

Unfortunately, and incomprehensibly, the same Echofon app, running on the big-screen iPad, makes life HARDER by insisting on TWO clicks to go from mentions to your favourite list. Fail.

On the Mac, I do use Echofon, but it doesn't have auto-completion, and it doesn't have "post with this tag". It does the rest so simply, that I stick with it.

On Windows, I'm all at sea... using Seesmic Web

Anyone have any recommendations for Mac, Windows and iPad that would satisfy this simple man?

Thanks,
Lee.