Hi TP, I've just gone the other way, always had MTBs but recently got a road bike to ride between MTB sessions - there's a road outside my house but a decent forest is a drive away.
Hmm, well there are pros and cons to each. A lot depends on the sort of trails you're going to ride, (and who with to some extent), and also how much you can spend.
Hardtails theoretically give you a better/lighter bike for the money, so if you're on a tight budget it is better to get a decent HT than a 'cheap' full sus. A hardtail requires less maintenance (good for winter, and for avoiding expensive servicing bills). Also, HTs are more efficient because you're not losing as much effort into the suspension (though some FS frame designs and posh shocks can alleviate this to a large extent).
Full sus gives the advantage of more comfort if you're just riding sedately, but when in attack mode the real benefits are better traction for climbs, 'off-roadholding' when descending, and less chance of falling off due to compression hits when jumping off stuff.
With suspension, (full sus OR hardtail) a simplistic view could be thus: More travel costs you pedalling effort, but can pay for itself in traction/grip. Also, more travel can compensate for lack of technical ability in trail-riding skills. I would say less is more, by which I mean you should try to get only as much travel as you need. Going bigger can cost more £££, more effort and more weight. Too little and you'll not get the full benefits.
For example, my first MTB was a rigid Saracen which the LBS sold me. They were only experienced in road bikes (as all bike shops were back then) and sold me a bike that was way too big. Great fun but I couldn't control it and hit lots of trees. Lesson learnt, my next decent MTB was a 1988 rigid Cannondale. Still no sus. Handled sublimely and with decent XT and Mavic kit it really rode well. I still have that bike as my winter commuter with slicks! Great for riding around the forest in 'explore' mode, and a good commuter too. Then I stuck some sus forks on it and found that it was more comfy and I could ride harder (ignoring for a moment the fact that the frame wasn't designed for sus forks). Eventually I decided I wanted to go full sus as I was getting keener on riding off-road. So I bought a Rocky Mountain Element which was a lightweight marathon bike which had about 2.5" front and rear. This was lighter than the (very old and solid) 'Dale and climbed well, as the back wheel gripped the ground when climbing. Also more fun to attack singletrack, jumping over small fallen trees etc. It also saw me right up in the mountains round Lake Garda. On the Lake Garda trip, the other lads had 'big' FS bikes with hydraulic brakes and at least 4" of travel, cf my V-brakes and 2.5". I beat them to the top of every hill, and they flew past me on every descent; where I was hanging on for grim death with massively pumped arms, they were flying down safe in the knowledge that their sus would cope with the bumps and the brakes would haul them up pronto. For the record, I'd still rather have a set of V-brakes than cheap cable-operated disc brakes found on very cheap MTBs. However, hydraulic disc brakes are the way forward if budget allows. No dispute.
I started riding with some lads from work in Bracknell forest, plus we did a welsh trail centre or two. At this point, I realised that for that type of riding, if I was going to keep up with these (younger, fitter and more skilled) riders I needed at least as much travel and some decent stoppers. I now have a Cannondale Jekyll with 5" travel and Magura Marta disc brakes. It wasn't cheap, but it instantly got me back in the game, rather than accepting that I wouldn't be able to keep up.
Hopefully that 'life story' will help you decide what sort of thing you're aiming at. It's getting the right kit for the type of rider/riding, at the right price. And of course the right size frame - you REALLY don't want a MTB that's a size too big. Happy shopping!
PS FWIW, if you're new-ish to mountain biking, try to get your advice from a bike shop that primarily specialises in mountain bikes if there is one near you. And if you will be riding with others, ask their advice, or see if you can get a ride on their bikes. I really thought I would love the Scott Genius, with 4-bar linkage and lockable suspension, and expected to hate the long-travel, single pivot Lefty-forked Jekyll. 10 mins on each bike changed all that - the Jekyll doesn't need all that stuff - so opinions and reviews are really only someone else's idea, you really need to try them if you can. Some shops will let you demo their bikes off road, which is a huge plus. And bear in mind that buying used MTBs can be a potential risk - they usually get a lot more of a hammering than road bikes. OK, there is a risk in buying a used road bike too, but I bought a used road bike and it had been obviously much-loved and is almost pristine even though it's a 2004 bike. A mountainbike that's been properly used but not properly looked after could have shagged suspension, bushes, drivetrain etc etc.
