I bought my 3DS XL from Game, this turned out to be an excellent decision.
Even if you are not trading in your original 3DS, there's lots of benefits here.
1: They will give you a free AC adapter with the system. Maybe this is at launch.
2: Console purchases come with a £10 voucher on the receipts. The one I received is good until the 10th of August.
3: You can get a GAME reward card at the same time for free. You get points worth 2.5% of the items you purchase. For the 3DS XL at £179.99, you get £4.50 worth of points. Points go on your card on the day of purchase and can be redeemed the next day.
With the £10 voucher and £4.50 worth of reward points (for the system alone), you can easily grab an eShop card worth £15, for just 50p.
I bought a 3DS XL and two games today actually, with some previous points on the same card, I can save more than £18 on my next purchase from GAME, it's awesome.