Photoshop has more options and the most tutorials are available for it. I prefer to use Fireworks though. It's like a hybrid of Photoshop and Illustrator. It gives you also more control over the objects.
i've never used illustrator much, but between photoshop and fireworks, i found back when i still used them that fireworks was much better suited for web design because you can manipulate everything as objects (so you can draw a box and easily change the width/length by just typing in the values you want) whereas in photoshop you can't do that to the same degree.
Fireworks is about a kazillion times better than Photoshop for web design. The absolute control of objects with or without the use of layers is amazing. Fireworks dosent have the learning curve required for Photoshop, but almost reaches the same levels of awesome in terms of raster graphics when you reach the levels of awesome. Plus of course Fireworks has vector, which already gives it a jump on Photoshop. I guess Fireworks is the brain child of Macromedia and Photoshop is the brain child of Adobe. Photoshop = digital art, Fireworks = web / UI design/ general purpose. A few years ago I did a university project where I switched away from Photoshop to Fireworks for design in a flash app and everyone else used Photoshop, five years on they are still using my project to show off what is possible in the Interactive Media class.
I asked a friend of mine who does web design and he said Fireworks all the way. He showed me some of his work and he does some amazing stuff in Fireworks.
Always used Photoshop and sliced everything, then used Notepad++ to edit the code... But I know most designers prefer Illustrator or Fireworks. Try them all out and decide what's the best and/or easiest for you.
I love photo shop. I've never had much trouble. Since its photoshop, I can also design all the graphic . I mockup my exact website in photoshop. Almost pixel for pixel.
If you don't feel like spending money right now, give Inkscape a shot. As much as I think Gimp is not even close to Photoshop, I actually prefer Inkscape over Illustrator for quick drawings.