Hi
I have worked in a Giant dealer selling these bikes, so here's my 5p:
Both bikes pedal very well. The anthem is quick going up-hill and in the right hands will come down quickly too (but slightly slower than the trance in the same hands). If you intend to do XC and trail centres, and have decent skill, I'd say get the Anthem X.
One point to note: the Anthem (90mm travel) is a bit snappier than the Anthem X (100mm travel) – the X is no heavier and has gemoetry slightly more suited to trail centres. You dont NEED more travel, the geometry is arguably more important. If you want to progress to more aggressive riding, slacker angles and more travel would be good, but then you would do well to look at Specialized Stumpjumpers with 120mm travel.
And my final point: if you do get a trance, there's no point getting a 100mm travel one, as the X is more capable yet weight the same or less depending on the year. The Giant rep actually said that, hence they dropped the standard Trance the following year.
Hope some of that helps, email in profile if I can help any more 🙂
Oh and it may be wise to wait for more frames to come up for sale if people get good Xmas presents! I wouldn't pay 650 for the second hand Trance frame unless it and the shock are MINT.