I've ridden bikes with the short one and the tall one.
I prefer the tall one. Having never carried a pillion (save Shawn - the Sheep) I don't really care about passenger comfort. However I have a sissy bag and it's enormous. It's easier to put on to the tall bar, it's easier to strap other stuff to and then use the rack too.
Paul has the short one on his and he wises he'd got the tall one.
Just get the tall one.
Gina
03 America - Pretty stock - except the TBS wheel...

06 America - missing, presumed in bits. With it's TBS wheel...

09 America - It's very blue....