For use with a Laptop....Smaller is better.....but it really depends on your screen size.
I have the Intuos 4 Large and just for the sake of it, I tried using it on my 13 inch Macbook Pro......near unusable......even though it maps the active area to your screen size....if the Active Area is bigger then the screen your using it on.....lets just say extremely awkward to use. ....I even then for the joke of it tried connecting it to a 8.9 inch netbook I had...
Conversely....the Intuos 4 large worked wonderfully with my 23 inch desktop monitor.
So unless your going to be using a 20+ screen....don't even bother with the Large or X-large size.
Intuos and Bamboo are both made by Wacom. The only way I could explain the difference between them is that Intuos is to Photoshop as Bamboo is to Photoshop Elements. Intuos has more pressure sensitivity and customizable buttons, also a spinning track to make brushes bigger, zoom, tilt the canvas and scroll through layers. Bamboo only has an awkwardly placed ring that I really never found useful with a tablet menu.
A bigger size is not necessary unless you're used to drawing traditionally on an enormous scale. This can actually turn out to be a disadvantage if you are used to drawing on 8x11 paper. unless you paint murals or something of similar size, the proportion of an ExLarge tablet will mess you up and it will be harder to learn to draw with it.
Both Intuos and Bamboo are compatible with both Mac and Windows computers with drivers available for both on the Wacom website.
It really depends on the program you will be using the laptop on. If you use Paint SAI, I would recommend a windows laptop because you would be able to use just about any program on a windows and SAI does not have a working Mac version. But if you prefer photoshop or AI, it really doesn't matter which you use if you are buying a laptop based on your tablet.
I would, however, reccomend a laptop with a larger screen if you are going to use it for art, or investing in a second larger monitor for drawing.
Bamboo are cheaper than intuos and if it is your first tablet, I would recommend bamboo, seeing that it is smaller, thus easier to adjust to digital art-making on. If you know what you're doing, an intuos is a great investment, but are much more expensive than bamboo products. I would not personally recommend getting one right off, but that's just my preference and I'm sure someone else would be able to present an argument as to why you should buy one right off.
I personally have owned both a Bamboo Fun and an Intuos4 Medium tablet. I usually create on an 8.5x11 to 18x24 scale traditionally and the Medium size has been just grand for digital smaller or larger-scale projects.
Well money really isnt the problem at all, but you see it just seems that I like to draw "bigger" and like I tried drawing on an ipad with a pen and it felt WAY to small and weird. I'm so confused <__>