The components are what are important. You did not mention the model for each bike, or whether it is standard spec, but if we assume a 2012 model with standard spec then you find the following:
The front and rear derailleur on the Raleigh are better spec. They are Deore with a Shadow (tucked further into the bike to help prevent hitting rocks etc) rear, or so it appears from the description I did find. The Silverback has an Altus front and Deore back but not the Shadow version, again from what I see online but you can confirm. In saying that, the front derailleur does far less work than the rear so the more important component here would be the rear in my opinion, in which case they both have Deore.
You'd then need to compare the shocks too. I am not particularly familiar with either so will not try to pick. What I can see (again based on the online specs) is the Raleigh has remote lock out whereas the Silverback has manual. Again, based on your needs this will be neither here nor there. Just to explain, lockout locks the suspension of the fork when you are climbing for example to prevent energy being lost in the fork rebounding. You'll probably find you hardly use it in reality.
All else being equal I'd choose the 27 speed over a 24 speed. Also the fact it is on "sale". But then I am also a fan of the quality of Silverback bikes.