Dude, you first of all have to decide what type of riding you are doing. For trail riding and singletrack stuff, a 26er will always be better than a 29er. If you are racing more and riding longer, less twisty stuff, then a 29er is your friend. I have a Trek Hifi Pro and a Morewood Shova, both very different bikes for different applications. I ride the 29er mainly on races and through the cane, but wouldn't ride it in Tokai a much as the Shova (if i lived in CT) for example. You can use both types of bikes for ether types of riding and each has it's benefits and faults, but it's horses for courses in this case. The efficiency and 'comfort' of a 29er is only really evident over longer endurance type rides. If you are riding 20kms etc, you aren't going to feel the difference and a 29er isn't like riding an arm chair compared to a 26er. It also isn't a wonder machine that makes you go so much faster and cures all your troubles, so don't get suckered into thinking that. If you do decide to go for the 29er, the Giant is the better of the 2 above for spec. the Hifi pro is a closer match to the Giant, but a bit more. You do get all X9/XT stuff though and the wheels are race ready and way better than the Giants. If you get either you won't be dissapointed and you can always upgrade your Giants wheels at a later stage if you want to go light and racy. Hope this helps?
