I am a fairly big fan of HTC, so I do not want to just say go with the Nokia. But there have been a ton of bugs and sub-par problems with the original Titan, so the 900 gets the edge to start. But I sure would look at the Titan 2 and see if:
1) Call quality is vastly improved. HTC usually has great call quality with their devices, which makes the Titan 1 and it's problems really strange. I am betting it is much stronger with #2, and then it is just if the 900 is better or not.
2) What does the 16 MP camera on the T2 actually bring? The camera on the T1 was outstanding. I am concerned that they are messing with one of the best parts of their product. We know Nokia has great cameras, so again just compare.
3) The HTC Hub is a good selling point, and Nokia is making a lot of it's exclusives available to all WP devices as part of it's support for Microsoft (truly is a win/win with this team up). So, while Nokia will have the best support, do not think HTC is a slouch.
Overall, if I had to choose sight unseen, I would pick the Nokia. But a few months ago if pressed, I would have picked the Titan over the Focus S sight unseen. Once I was in the AT&T store in Champaigne IL testing them both out, the Focus S was easliy the best device for me. I am not saying the 900 isn't the clubhouse leader, I am just saying do not write off HTC, which was the standard bearer for WP long before Nokia got the flag.