Front-page will allow you to create something great if you have the design skills and html experience needed.
iWeb will allow you to create something great if you don't.
Front-page allows more 'freedom' as long as you know what you are doing, if you don't you could end up making something that despite iweb's limitations, looks a damns site worse.
iWeb is cheaper, and comes on your mac as standard, so you can always use it and if you find it not suitable, then get front-page via parallels ( or bootcamp)
iWeb would be my choice.