As far as flexibility, I would actually prefer the bracelet models when it comes to Panerai Luminor. That's mainly due to the fact that you can always put a leather/alligator strap to any bracelet model but can't quite do the same if the other way around.
I do agree w/ Anthony that for formal occasions, an alligator strap is probably more suitable. However, for casual occations, especially when you engage water sports, then I'd appreciate bracelet as a viable alternative to rubber strap.
There's obviously no denial that from a historical point of view, calf leather strap is the right way to dress up your Panerai but then again, we all need a bit of variety in life don't we?