I really like Note Taker HD as well. It magnifies like upad as well. I think between upad, noteshelf and note taker hd all three appear to be very strong. I have no used upad or noteshelf yet, curious to see what the main differences are between these three apps.
I tried using Note Taker HD for awhile, but I didn't like it as much as I liked UPAD (which I only had the trial for at the time). While I do think Note Taker HD is slightly more powerful (though that's arguable), I felt that UPAD's user interface was light years ahead. Note Taker HD's GUI just isn't up to par with its functionality... And that killed it for me. I do however believe there are a good amount of areas UPAD could improve in, but that's probably a discussion for a different time lol