It's all about what suits YOU personally. Nobody can really tell you what's "better". What I can say is that having a revision C 12", the heat issue is solved. It gets warm, like any modern laptop, but definitely not *hot*.
Edit: I just read the question about Photoshop and Dreamweaver. Honestly if those are large concerns then yes it will be cramped. I've tried both, and they do seem pretty cramped at 1024x768 which the 12" runs at. For things like that I'd be inclined to pick the 17" if I could afford it. 15 would be a compromise.
It's all about the balance between portability, price and what you want it to do. If the Photoshop and Dreamweaver outweigh the desire for a cute portable laptop and you have the extra money to burn, go for the larger models.
My experience is:
I wanted a 12" for the portability and price but was worried about the 12" display size. It seemed tiny. Yet once I used it, I was delighted.
If you're concerned about the display size, ask yourself: are you comfortable with 1024x768? Lots of computer geeks I know run at much higher resolutions and would hate 1024. Personally I ran at 1024 for many years on my PC desktop and am used to it. As a matter of fact I *prefer* to look at the 12" TFT than the 17" Iiyama CRT running at 1024. It's THAT good. I was blown away by the clarity, and if you're already happy with 1024 then I can as good as guarantee that you WILL like it. I have never felt that it's small, ever, even in dual-display mode next to the 17" CRT.
If you're concerned about gaming (except for occasional use), get the 15". At least, that's what I gather. As a user of 256MB at the moment all games and everything are slooow anyway, but the difference in graphics card for 3D performance is apparently quite significant.
You don't get PCMCIA on the 12". Would you miss it?
(I wouldn't - I had a modem card, network card and wireless card for the PC laptop, all of which are redundant with the built-in features)
Do you need Firewire 800? (The 12" "only" comes with the super-fast 400 instead of the blazingly-fast 800)
I say 12" for the portability and price, but if you're bothered about the above things then get the 15".
Either way make sure you get a 5200RPM hard drive (I didn't due to credit refusal from MNBA - I had to buy from PC World and get the 4200 but hear it's MUCH faster) and as much extra memory as you can afford as 256 is, quite honestly, pathetic
