What is it that you want the bike for? If it's for commuting, cycle track, farm/forest trails and some mild off roading you simply do not need a full suspension bike. In fact most of the time it's questionable whether you need a front suspension fork!
What you've got to remember is that everything extra that's bolted to a bike is extra weight that you've got to lug around. A suspension fork might weigh over five pounds, maybe five times what a simple ridged fork weighs. Look at all the parts on the rear suspension and think about what that lot weighs!
These things also cost more money which means that money has to be shaved off elsewhere. So a £300 hardtail, all else being equal, will have better components than a £300 full suspension bike. The better components will work better 'and' probably be lighter!
Perhaps the best way to understand it is to look at the very cheap full suspension bikes you can buy from places like JJB Sports and
Halfords for about £100. Think about how little the components on the bike must cost if the whole bike costs £100 !! These bikes weigh a ton and everything on them is poor quality. If you ever do manage to drag their bulk over some rough ground the suspension will kick you all over the place and even on tarmac it'll turn your best peddling effort into bobbing and pogoing slowly along the road!
The bearings will last about a week and the cheap disk brakes, because that's what everyone wants these days, will give you nothing but grief as they squeal and clunk their way to a stop.
With bikes, less is often more. A lightweight hardtail, or even a bike with no suspension at all, will be faster, more reliable and more fun to ride than a cheap full suspension bike.
