Depends on your area. Check out what stations are broadcasting HD, whether you listen to them, etc.
The subchannels generally are not worth it except in a few cases - they know people don't listen to them, so they really just don't care yet. The quality on the main channels is often worth the cost by itself.
If you don't listen to radio stations that have an HD stream, it's not worth it.
There should be no difference where the HD tuner is, and in fact since the chips are the same in all HD receivers, there should be almost no difference between brands too.