Well, the value and the tremendous sound come from the 70's versions, and I'm a VERY big fan. But I would recommend playing one before you plop down big money. The reason I say that is the nut width is a little narrow, and the necks are a little thin for a lot of guitar players (but I love them). Another reason is that the early 70's versions had a neck angle that is parallel to the body. If you're used to the feel of a gibson, where the next is angled back a little, you might not care for the early 70's versions. Also, this configuration means that some of the guitars have bottomed out bridges (where you can't lower the bridge anymore, but the action is still a little high).
In my opinion, the "magic" years were '76 and '77. On those, the neck is swept back, the bridge is nice and high and the string tension is improved.
The 90's versions are great guitars, and the necks are usually a little beefier. Most of them came stock with a set of Duncans. they are great pickups, but they have more of a mid-range quack to them, and really disappear with the tone controls rolled down.
I'm sorry to say it but the first reissues from a couple of years ago were crap. the body does not feel resonant and the mini-humbuckers were fouled up. the neck version sounded pretty good, but the bridge mini-humbucker was piercing and thin. It might be the worst sounding guild I've ever played.
But the NEWEST-newest ones took the good fit and finish and added color options and a re-issue of the 70's HB-1 pickups. It's been driving me crazy that I have not had a chance to play one of these guitars. but I bet it's the closest thing you'll come to the "classic" S-100. Add together the fairly generous return policies most sellers have, the inclusions of a lifetime warranty, and the money you save vs going vintage, and this is what I would buy as my first guild solid body.