I was where you are and went with Sandvox. This software can import old iWeb sites, but with varying success.
As far as the Sandvox itself is concerned, I am very happy with it. Nice interface, fairly straightforward and easy to use and seems to do everything iWeb did (and more). And great support from the developers and some nice third-party add-ons.
It was a fairly smooth transition for me. Your mileage may vary.