Some web designers prefer Illustrator/Photoshop, others Fireworks, but really either is very powerful for web development. Fireworks has a few handy features for web development (apparently some slightly better ‘save for web’ options, for example) but TBH, I don’t use it at all, as I don’t feel I need it, and it’s just another thing to learn. I’ve never needed anything from Fw that Ai/Ps couldn’t do.