Hi Erin,
You will love STS. Either way is fine. I actually have the downloads and the DVDs. I had the DVDs first and ended up getting the whole library when they first released downloads.
If you are thinking of taking your workouts to the gym, then the downloads are useful. Also, with the downloads, you can make any new workout you want. I made some really nice total body STS workouts with chapters from the downloads. I have a preference for the downloads now that I am used to them. I did have to get the cable to hook my laptop to the TV.
As for the DVDs, one thing that I like that is not on the downloads is that you can have the workouts without the music and use your own music with it. It makes for nice variety. The downloads have the music from STS which I personally am fine with. Cathe works you so good you are focused on what you need to do
When I got the DVDs they came with the guide. I never used it. I used the 1RM in the workout manager and printed all my workout cards that way.
I don't know about your strength but you might find yourself needing to buy some weights as you get stronger. And you will get stronger. The first time with STS will blow your socks off as far as the weights you can lift. I did get the tower which is very useful for pullups/chinups and also for barbell chest press exercises.
I hope this helps.
When you get the program, just get started and all the confusion will go away.
Helene