to be honest i have not found the perfect option. all of the SBCs i have found have some trade off.
so i'm currently experimenting with the Hammer board from TinCan tools. http://www.tincantools.com
it uses Embedded Linux as it's OS.
while it's a great option if you know what you are doing, i would *not* recommend it for a complete Linux noob.
at the moment there is little in the way of documentation or support so you are largely on your own when you want to do anything other than install a basic OS.
it looks like it might develop into a great product once a few people document how to do some of the more complex tasks though.
one of the advantages of the NSLU2 is it has a huge developers community and it runs the Debian Linux distribution which also has a huge user base so any problem you run into and there should be an answer on the internet somewhere.
on the other hand, the TS-7260 is a commercial product and you can buy it with Debian pre-installed so in theory you should have a very stable platform there with the manufacturer and Debian community for support.
there are a few on the forum who use the Gumstix boards. like the Hammer board these use a somewhat obscure linux distribution so you will have to rely on the Gumstix developers community for support.
i believe there is a reasonable selection of pre-built packages available for the Gumstix so it may be an option if you don't need any obscure software.
as you are new to Linux and want a Linux based board personally i would recommend going with something that has a mature Linux distro (like Debian) as this will make installing packages far easier. you will be able to just download and install most of what you need.
i would also recommend installing Debian on an old PC so you have something running the same OS to develop on. this way you can work out how things work on something with a monitor and keyboard....
so yea, i guess i'd recommend either the NSLU2 or the TS-7260 for ease of use. (the word "ease" being relative...)
the TS-7260 has lower power consumption and more I/O options so if you need any of those features that would be the best bet.
having not used the TS-7260 i don't really know but it looks good on paper.