Best for what?
There's really only two different multitools in the Swisstool line. The other variations only differ in an individual tool or two.
The Swisstool is a beefy full sized multitool.
The Swisstool X version has scissors instead of a serrated blade.
The Swisstool RS has scissors and a seatbelt cutter instead of a file and serrated blade.
The Swisstool CS seems to be the same as the X with a "plus" package.
The Swisstool Spirit is a completely different multitool altogether. It is a smaller, lighter, and more ergonomic multitool with slightly updated tools.
The Spirit X has a traditional SAK-style plain edged knife instead of the "butter knife" blade (the serrations and lack of a sharp point make it resemble a butter knife blade, although it is very sharp).
The Spirit S has the traditional SAK-style blade instead of scissors.
Both models are available in a "Plus" package. They come with a wrench, corkscrew, and some hex bits. They add a lot of bulk to the sheath. There is also a set with a ratchet instead of a wrench.
Some black oxide variants are also available instead of polished.
You may also wish to have a look at this:
http://forum.multitool.org/index.php?topic=12075.0
If you need a full sized multitool, get one of the Swisstool variants.
If you want an EDC tool, get the Spirit.
The rest comes down to how you feel about serrated blades and scissors, more or less.