What are you wanting to do with the Sheeva?
How familiar are you with Linux?
I think that getting the basic is a good idea as it seems everything that is done on the higher packages can be done for free, using instructions on here, anyway... Though I'd (a) be a little worried about messing up and (b) like to make an image of the SD card if I got one with that so I could back up in case I do mess up. I assume there is a simple way to image the on-board flash if I buy the basic model however I don't know what that is yet.
I'm hoping to use Sheeva to, initially install Tonido and use their software to easily access my work. Normally at the moment I carry a pen disk to Uni with me but actually work on a machine there and a local machine at home. Keeping things in sync is a pain so being able to always access a "latest" version would be good.
Beyond this, I'd simply like to experiment... There are a few cool things I've seen. I'd like the idea of trying out SSH and also trying to set a Squeezebox server on it (Hopefully getting a Squeezebox for Christmas). The idea of VNC is also something I'd like to try.
I'm not all that familiar with Linux. I've used it in fits and starts, with my latest attempt messing with it on my EEE PC. I actually got pretty reasonable (Obviously no guru) when doing that but once I'd got it set up how I liked it, I never messed with it anymore and then that was that. I did try to run a mail server on a linux server at Uni however that setup was too old and didn't have the packages I wanted, I wasn't allowed to install what I wanted and so that never happened. I guess I could also play with mail servers on the Sheeva too...
I guess what I'm saying is I'd like to use it as a Linux educational tool that also servers a functional purpose, too.
The preconfigured options are best for those that don't want to be messing around with U-Boot and the installer. At the one extreme, Meteohub is almost a turnkey solution, and this config is aimed at the less technically able Meteohub user.
We suppose that in some cases our customers have the ability, but might not wish to spend the time learning the necessary procedures.
It seems to me that the fact you have signed up here, and are asking this question (and in particular "I'd simply like to experiment..."), suggests to me that you are someone that is prepared to work through the learning process and do it yourself. You'll find help here and on the wiki, and we can offer advice through the New IT forum too. You'll learn a lot, and enjoy it a lot by doing so.
Declaration of interest: I am a New IT employee.