They were all pretty high spec new bikes. Giant had a demo day through a LBS at a trail. I regret not getting there early enough to take a TCX 0 or TCR AdvSL4 out... but my priority was obviously MTBs, so I rode a Anthem X Advanced 29er 1 and a Trance X 29er 0. Both had full XT groups. The Anthem had a Rockshox SID and Monarch RL. The Trance had a Fox Evolution CTD fork and shock. They were both running way too high pressure in the tires-- Nobby Nic 29x2.25 on the Trance, Racing Ralph 2.2 on the Anthem. I rode the Trance a full lap and almost washed out a few loose-over-hardpack corners. I rolled away from the start and dropped the Anthem down to 28F/32R -- much better, but still very safe for any rider heavier than me to not bend a rim.
They estimated sag by airing the fork and shock on the stand based on my weight. Good enough, I guess.
They both climbed well. I rode the Trance in trail mode, and the Anthem open. The Anthem did have some pedal bob when I was jamming 15-20mph in open flat ground, and I could feel it even more during short standing climbs. The Anthem's steering was noticeably faster and tracked better. Both of them ate up the roots, but there aren't any rock gardens on this trail.
I noticed the XT brakes had great modulation but seemed to have a few mm of takeup slack in the levers before doing anything. My bike has Magura MT4s which have no such slack, but they can put you on your head if you aren't careful and they howl when I brake hard. The Shimanos were silent.
Today I rode my dad's 2012 BMC Speedfox SF01 26" at the same trail. It has the same running gear as the Trace X-- Shimano XT and Fox. I had the advantage of setting the sag properly, along with tire pressure and other little tweaks. I noticed right away, sitting next to my bike, that it has a long wheelbase and long chainstay. To my surprise, it climbs well. Better than either of the Giants. The suspension linkage looks *very* similar between Giant and BMC. Certainly different than my Santa Cruz's 1st gen VPP. I did the whole trail with the Fox RP2 shock in open mode. The BMC accelerates out of corners very much like a hardtail.
I noticed that the BMC has a low bottom bracket. Probably the same height as my Blur originally was, with a 100mm fork, but I have a 120 on it now and the BB is about 1/4" higher. I did scuff my pedals a few times, actually, something I never did on the Giants and rarely do on my bike. I did get more laps on this bike so maybe I was carrying more speed in the corners, despite my dislike of the Rocket Ron 26x2.25 tires. They are way squirmy cornering fast on hardpack and I actually tore a knob on the rear tire.
Another thing I noticed is that the BMC is very nimble. It turns better than the Anthem, without being twitchy. The BMC accelerates well out of corners too. Also the BMC is pretty fricken huge for a large. My Blur is an XL and has a shorter top tube, and same head tube. The Anthem was an XL and it was slightly bigger- probably the biggest I could possibly ride. I'd buy a large in that for sure. The Trance was a large and definitely felt smaller than the Anthem or BMC.
All of the bikes were very, very good. I would be happy owning any of them. I was surprised that I liked the BMC the best. --Actually, I like my own bike the best, but it has a better fork and shock so you have to exclude that a bit. My frame itself, however, is definitely not as good as the BMC. I did not get the impression that the 29ers were faster because of their tire diameter. I did get the impression that the Racing Ralph is a fantastic hardpack tire, and the Rocket Ron is not. I reserve judgement about the Nobby Nic because it was so overinflated. I am not sure if the BMC is the most nimble just because of the way it is designed, tuned, or if it just fits me better.