I would rank them like this:
Ruler Designer:
I like being able to make my own dynasty named after myself, or whoever I want, so this is a fun addition. I just wish we were allowed to use it on more than one ruler in a game, and I also wish it could be used while loading saved games in case I decide to switch and play a different nation mid-game.
Music/Portrait DLCs:
Get what you want based on budget and how much you think the game is worth. These have no real effect on gameplay but at least you get to see and appreciate them no matter who you are playing. (Actually the music ones might be region/religion dependant.)
Sunset Invasion:
If you don't like the idea of being invaded by Aztecs, then skip this one, but as far as I'm concerned this one is the most enjoyable because it actually has a pretty real impact no matter who you are playing (especially so if you are actually playing a crusader state).
Sword of Islam:
This one will have no effect on your game whatsoever unless you actually want to play a muslim. If you do not want to play a muslim, there is no reason to get this, except to avoid accidental game-overs when your heir or yourself accidentally becomes muslim. It could happen.
Legacy of Rome:
This one is even worse than sword of Islam. Many of the additions won't affect you at all unless you're playing specifically the Byzantine Empire. The one major feature that does affect every nation is Retinues, which I believe to be the worst addition to the game so far, considering it completely demolishes any semblance of balance the game had before.