If you are happy with iWeb, I would keep using it until something better appears. Its just a matter of time!
Freeway Express has been around for a long time and is overdue for a rebuild. I wouldn't recommend it in its present form.
RapidWeaver and Sandvox are the main contenders. RapidWeaver can work out very expensive when you start to add all the extras. Sandvox is rather limited and not nearly as intuitive as iWeb.
Quick 'n Easy Web Builder is the nearest to iWeb in price and has the added advantage of being cross platform.
Flux combines drag and drop with the ability to use code as well but is over complicated.
Fraise, Taco and Rage's WebDesign all require that you learn some code which is not the giant step that it appears to be. These apps will allow you to build much better websites than the drag and drop style but will require quite a lot of learning.
If you don't want to move beyond the skill level requied for iWeb. Hold off until its replacement appears.
iWeb doesn't produce poor code - just a lot more than is necessary. Its better than its rivals in that respect.
In the main, poor download times are more to do with the users ignorance of optimization, the over use of graphic elements and not taking the time to learn how to present movies and music in a better way.
I haven't built a new site with iWeb for almost two years now but use it to maintain existing sites.