Intuos is better in terms of sensitivity and general feel to it (at least from my expirience; I own a Bambo and have tried out Intuos 4 in store). But it's also much more expensive, so if you'd rather spend less money, just buy the medium Bamoo Fun. I have a small one and it's pretty great.
Ask yourself these questions! 1: what can you afford? makes the choice easier Bmboo is the cheapest line of wacom, works well for the casual hobbyist Intuos is a better line, more settings and sensitivity. but a lot more money! if all all you can afford is a bamboo then buy that.
2: What do you use it for? Are you planning on becoming an artist? If yes, and you can afford to, get the Intuos line. It will be worth the investment INuos is a better tablet..... Keep in mind however! There are artist out there that do incredible art with a cheap bamboo. So the tablet is not going to make you a better artist, it's just a tool, some tools help you do the job a bit easier, and maybe a bit faster is all.
3: As to the size? What ever fits into your budget? and again what do you intend to do with it and where is it going to sit? Got a small desk space? then maybe the smaller tablet is better? got a laptop and plan to travel with it ? smaller maybe better Is it going to stay at home with a desk top computer and you have a good size desk? then maybe a medium or lager size tablet is a good idea! What size is your monitor? The bigger the monitor the better off you are with a larger format tablet as the ratio to movement is better In other words a small tablet on a 30" monitor, will fly across the screen in a very small movement, makeing it hard to do long pen strokes and larger tablet the movement will be larger to cover the same space on the monitor making it easier to draw out long smooth strokes. This is better for drawing and painting for most people!
Get a tablet that corresponds with screen size. If you have a small work area on your computer, there's no sense buying a giant tablet. I think the total work space I have on my 13" laptop is maybe 5x7" (because of my Photoshop tools and menu bars and stuff), and I have a small Intuos3 (4x6") and it does just fine. On my 21.5" monitor, my tablet is a nightmare.
The Bamboo can more or less accomplish pretty similar things as the Intuos. I'd either go for the Capture (smaller, $99) or the Create (bigger, $199), considering that even though Capture has pretty similar features to Splash and that other one, it comes with better programs for considerably less money than those programs are on the market.
If you can afford a bigger tablet, I would advice you to get a bigger Bamboo or Intuos. However, if you are like me and don't really like the idea of spending few hundred euros on an Intuos, I'd fall more on the favor of a bigger Bamboo. I bought myself the most basic Wacom Bamboo (the one that costs like 60 euros or so) and while it's more than enough for me at the moment, I might go for a bigger one in the future. One thing that bugs me about the basic Bamboo is lack of clear support for pen nibs and protection sheets. I had to tape a piece of copy paper on top of my Bamboo to protect it from scratching :/
Looking through a Finnish electronic sales site, there doesn't seem to be any clear advantage on the bigger and WAY more expensive tablets, namely Intuos. The lack of protection sheets for the Bamboo is lame but as I said, you can try taping a piece of paper on top of the drawing area. I stopped doing my lineart digitally since my wrist wasn't really up to the task so the taped-on paper doesn't bother me at all. I can't see any kind of difference when painting digitally. Pen pressure might be a problem but I guess you just have to ask around how other Bamboo owners solve their scrathching problem.
Looking at the site Wacom Bamboo Fun Pen & Touch Medium CTH-670S seems to be the only rational choice if you want a bigger drawing area. However it already costs 200 euros. The jump in price seems somewhat high. If you have extra cash, then I don't see why not but if you really have to consider this as an investment, you'll do more than fine with the basic Bamboo IMHO.
Intuos has higher pressure sensitivity, but, that being said, there's really nothing you can do on an Intuos that you can't accomplish on a Bamboo tablet. People make great work on iPads with pressure-sensitive styluses that have lower pressure sensitivity than the Bamboo. I have a friend who continues to use a tablet well over seven years old and it functions fine, and I can't imagine that a refurbished Bamboo tablet wouldn't be on par with her nearly-decade-old tablet.
Honestly, a fifty buck bamboo tablet will probably suit you just fine. Get it refurbished. Any scratches it comes with you would have put on it anyways after a weeks worth of use. Tablets are nice things to have, and the larger ones are more convenient, at times, though not essential. Don't blow all your money on a large tablet because it wont really make much of a difference unless this is a professional investment and you intend to be spending most of your time on it every day. Fifty on another bamboo versus 300+ you'd be spending on the last model of Intuos isn't really worth it in my opinion. I have a medium sized Intuos (wired. Who needs a wireless tablet? How far away from the screen are you drawing?) and a Bamboo tablet and I've noticed no significant difference between them.