It really depends if you want portability. If you don't need to carry around your computer I'd go for the iMac. Better screen, less heat, better keyboard/mouse. I have a macbook, and if I didn't need to carry it to school I would've bought another mac mini.
24" iMac of course. If money is not the object - pleasure is. Go big. There are lots of laptops you can buy for the portable solution. Unless you are very mobile with no home base. I would never buy a leading edge laptop for pleasure. For business it makes sense but if personal then the large screen makes sense. Unless you live in a closet and space is a premium them the 15 or 17" iMac might fit...
To rephrase what gizmo said, look at your habits and what they're likely to be over the next couple of years. Do you like having a computer with you away from a desk? Are you in classes where you can use a notebook, or expect to be soon? If you answer "yes" to some or all of that, you're probably looking at getting a MacBook.
But ponder the necessity of a black MacBook - all it has is the 120GB drive and the black paint. If you think you'll want more than 80GB of storage, it might almost make more sense to get the 2GHz white model and buy a Serial ATA notebook drive yourself from a computer shop. I know RB Computing will sell you a 160GB 5400RPM drive for $204 - about the difference in price between the black and white MacBooks. It's easy to add in, and you effectively get a spare 80GB hard drive in the process.
You will probably find both do an admirable job of being awesome.
Portability comes at a price, and the real value is in the iMac. If value for money is a concern, and you decide to go portable, then go for the mid-range macbook, as the extra cost for the black simply isn't worth it.
Dollar for dollar, though, the iMac is where it's at. And the 20" is a beautiful machine. My brother just got one, and it's magnificent.
I have the 17", and it's been a stellar performer.
I'll echo thejst's comments and suggest the 20" iMac if you don't have a need for portability. Two features it has that are much better than the MacBook are the ATI X1600 video card and a 250 gb 7200 rpm hard drive. Both make for greater speed, and the 20" iMac display is great. I'm not a fan of all-in-one Macs and I had originally planned to buy an Intel Mini, but when the iMac came out with the Core 2 duo chip and the Mini didn't, I bought the former.
20" iMac 2.66 ghz Core 2 duo, 2009 & 2012 mac minis and 2013 13" MacBook Air
One of the reason that i still have go make my purchase is because kind of waiting for iLife and iWork '07 to be announced. I thought Steve would announce them last week and i guess not. Some people are saying they mat be announced this week.
It's application from Apple. I would definitely show my support by purchasing them. But if they are so close to be out in the market, i'm thinking to save myself some money by wait a bit longer.
24" iMac, or even 20" iMac is so beautiful. It's something MacBook can't compared to.
Even though I reply ur question on the other site, but I guess it's also not a bad idea to have a English version here...
I had both iMac 17 and MacBook Black. I had the iMac because I want to try it. Load it with the 1.5GB RAM it makes me really happy for a few months until I realize what I really needs are the laptop for portability.
At first, I thought I will do all the major work on iMac connecting to Dell 24", and I will transfer the file from iMac to MacBook if I want to take it out. After a few day I realize not only the 17" is really "not a lot faster", but also transfer the files take even more time than doin' all the work on MacBook.
So I decide to sell the iMac and keep the MacBook. MacBook connecting with the Dell 24" did slow down a bit. But it is still at the acceptable range.