The best Tangerine Dream compilation is still Dream Sequence. I bought it originally on a home recorded Denon tape, with an incredibly nice dynamic range (you'd be surprised, when listening to it on my Panasonic walkman). In the same charity shop, I one month later found the almost pristine triple LP set (along with Flashpoint), probably the source of the tape. That was in 2002/3.
In 2009 I bought the original Virgin double-CD in a now closed Copenhagen record shop, called GUF. The re-issue from 2000, I recently found for a few Euros in Musikpalast, Flensburg. The double MC version appeared last month on eBay, and I simply couldn't resist.
Dream Sequence is the best way to introduce a newcomer to TD. When I bought the Denon tape, there was also a Metal cassette of Poland, a vibrant recording of Underwater Sunlight and even Encore. But having Rubycon, closely followed by Ricochet and Stratosfear, bought on LP, the missing link was that mentioned compilation.
Whatever version you get, you will also notice the somewhat increased sound quality. Dream Sequence is the best introduction to TD...unless you buy a copy of Rubycon, in the same state of ignorance as I did in 2002, thinking music couldn't develop any further.