If it's a bathroom used by overnight guests, I think you can't have enough bars and hooks to place bathtowels after showers. Personally, I don't think towels get enough air on hooks, so they don't dry evenly.

Personally, I prefer hooks - They're much simpler to use and don't load up w/ a clutter of used towels, etc, and you can use them for not only towels, but robes, swimsuits (post-jacuzzi/swim), hanging toiletry kits, etc...
...tho if you have existing towel bars, there's no reason you can't add a line of S-Hooks onto your bars to achieve a similar effect.

What I particularly dislike are Towel Rings - IMO, they're the most difficult/inconvenient things to use on a daily basis.

Definitely a custom choice depending on your situation. Sorry for the delayed response, you probably already made your decision last year ;-)