First off, only a select number of films are available in HD...
Second, make sure you have a super fast internet connection or you won’t be able to watch in HD anyway...
Third, I believe NetFlix HD is at 720 - if you have a 32 inch TV, you won’t be able to tell the difference.
If there would be no noticeable difference, then maybe the Roku HD would be the best choice after all. I would miss the Youtube option. But price-wise, the Roku can’t be beat.