On top of "saaz vs tettnanger" Google search (http://www.scientificsocieties.org/jib/papers/1997/1997_103_4_239.pdf
Analyses of essential oil from 16 samples and a-acids and p*acids in samples of Tettnanger hops
grown in the USA showed that they were not the same as Tettnanger hops grown in the Tettnang
district of Germany. The composition of the essential oils and ratios of a-acid to (3-acid in samples
grown in the USA were consistent with them being the English variety Fuggle. Samples of USA clones
of Tettnanger and Hallertau mittelfriiher grown in Australia also appeared to be Fuggle but
commercial sample of Saaz grown in Yakima was similar to Saaz grown in England, at Wye. The
varieties Saaz and Tettnanger were indistinguishable by chemical methods.
Basically, its not just the variety that determines the hop, its to a large part also growing region. Somewhere else I remember seeing a report that Saaz and Tettnanger are genetically identical.
Based on that I'd say go with Czech Saaz. US grown Saaz is for breweries that need to keep and eye on the hop price.