I like
Howard. It's in that sweet spot right now - everyone is familiar with it, it's easy to spell and pronounce, but it's neither overly trendy or too dated.
Howie as a nn would cutesy it up for a baby, and he could grow into
Howard as he got older (although I love old man names on babies, so a baby
Howard is plenty cute on its own!).
All of your others are good too. All of these are good, solid, classic, masculine names.
James is probably my favorite, but
Douglas is good too (for a lot of the same reasons I like
Howard).
Ian is probably my least favorite of them, but it's still a fine name.
The double D in the middle of
Howard Douglas has a bit of a speedbump feel to it.
Howard James sounds lovely and distinguished to me. Again, though, all good choices.