Tingathat is correct they will be beaten to death. if you plan on putting money into a bike on the parts side realize that parts sold seperately arent cheap. just to get a decent fork and wheel set you're already going to be paying the price of a nice new hard tail. when buying used bikes take a look at the fork, wheel set and frame. the frame is most important. look for any stress cracks (especially around the dropouts, seat post and bottom bracket) dents or chips.
I've done the hardtail thing and don't want to get back into it for trail riding (although I may buy back my Black Market Riot from my brother).
I used to be super into riding and was a mechanic for a while so I know what to look for when picking up a used bike. I also have no issues doing my own work and things like replacing bearing/bushings/seals/etc don't bother me.
division.bellWhat's your budget?
Will you be riding bike parks/lift accessed terrain?
Climbing/Descending breakdown in %: 50/50? 30/70?
How long are your typical rides?
Are you content on 26" wheels, or are you into the hype surrounding the 27.5"/29" wheels?
Unless you personally know the owner, I wouldn't buy an older full suspension bike. Technology has grown leaps and bounds since the bikes you listed above, not even going into the frame/suspension/bushing maintenance or replacement. You can easily find something better, just depends on what exactly you are looking for.
My budget is MAX $2000, but looking for something closer to the $1500 mark. Like I said above, I used to be a mechanic at one of the local shops and enjoy working on my bikes (everything from bearings/bushings/seals to building/truing wheels). That's why I'm looking for something older and will upgrade parts over time. Also, knowing me, I would be upgrading parts whether I bought a $500 hardtail or a $5000 AM ride. I'd like to stick to 26 or MAYBE 27.5, but not 29.
Like I said, I haven't ridden in a long time and it's been even longer since I've gone trail riding. I live in southern Alberta (a couple of hours east of Calgary). There really aren't many trails where I currently live, but plan on doing lots of trail riding in the Calgary/Canmore/Banff area. Foothills/rockies. I don't plan on doing much lift accessed terrain, but it may be an option on occasion (I haven't before, but I'd like to try). Because I'll be travelling a bit further to get to decent trails, rides will probably be longer and about 50/50 climbing/descending.