I presume you are referring to iWeb, the WYSISYG editor? I recommend you stay away from it. I'm a fan for ease of use, and Dreamweaver does that really well, but iWeb really sacrifices functionality to obtain its ease of use. Of course, there are many workarounds to get past its limits, but I wouldn't head down that route. Dreamweaver all the way.
Also, don't plan on using Adobe Contribute if your site is created with iWeb!
-Louis