I'm looking to get my first mountain bike since I got my drivers license 15 years ago! I'm looking for a CHEAP full suspension 29er with disc brakes that I can use to get into better cardio shape. It'll be used mostly on the street riding with my wife on her beach cruiser, but eventually I'll take it out onto some simple desert trails around the Phoenix area. I'm 5'8" 208lbs and haven't ridden in a long time! Right now I'm debating between a Mongoose Impasse R2780 (Mongoose 29 ER Niner Mens Full Dual Suspension Disc Brakes Mountain Bike Silver | eBay) and an Ironhorse Sinister 6.1 IH7082 (29" ER Niner Mens Orange Black Disc Brakes Dual Full Suspension Mountain Bike | eBay). I know these are cheap bikes with entry level components, but would either one be better than the other? I'm leaning towards the Mongoose for both looks and brandname from my 90's BMX days lol. Also, I think I'll prefer the twist shifter over the lever on the Ironhorse. Any feedback is greatly appreciated. Thank you!

Honestly? I would highly advise you to avoid both like the plague. But if you really must buy one of them like your life depended on it I would opt for the Iron Horse. But that's like saying I choose having swine flu over malaria. The Iron Horse at least has a fork that isn't sourced in house, though being a low level Suntour doesn't boost it up much. Look in the used market.

Please: you're making me feel ill.

Perhaps someone could suggest some bikes to look for instead? Maybe used?

To the OP: cheap suspension forks are not a good idea - it's generally thought better to go with a rigid fork or a used bike. Oh - but you want cheap FULL suspension? Not a good idea - the handling will suck. You'll find the bike harder to steer, harder to turn and brake precisely - but easier to crash and more likely to break down. Unless you enjoy bruises, sprains and wasted effort, then go for a hardtail or all rigid bike. Or spend big bucks.

This is actually very helpful! I never would have thought about the full suspension changing handling. I was just wanting a softer ride for my out of shape fat a... oh well

Are all Diamondback's good bikes? I found a couple hardtails used on Craigslist for under $400 ...

Just trying to make the point clear, hard to recommend used bikes if you don't know where someone is located either.

No, not every Diamondback is a good bike. But some certainly are. You could post the links for the bikes and we will be able to give you some feedback if you would like. Going both used and hardtail will certainly get you much more bike for the money.

Getting suspension to handle well is very tricky engineering. Just a decent fork is $400-$500.

But for the type of riding you describe, you'd don't need it. Fat tyres at a reasonable pressure will do what want:

Balloon Bike

Get an all rigid bike and fit the widest Big Bens that will will squeeze in and then run at the lowest pressure you can get away with.

Well, I can't find the one I was talking about again. They must have sold already. However, I found a different one that is full suspension. Diamond Back Full Suspension Mountain Bike GREAT Condition

That is definitely a much higher quality bike, though definitely older. Probably late 90s, the components on it are way above what you would get on the low end newer models. I'm not sure what your craigslist market is like there but the price seems steep to me. Personally I wouldn't mind riding that rig at all.

What sort of riding do you intend on doing?

I'd like to work up to this: https://www.youtube.com/watch?v=-WCJxDyFzkU

... obviously not the whole 20 miles right away, but maybe in about a years time!

That Diamondback may be a little undergunned on that trail. You could probably do it, but some of the descents will be a bit squirrelly. That trail does look pretty sweet though.

Just out of curiosity, what part(s) of that bike make it undergunned and/or squirrelly?

The parts on it are pretty high quality, that isn't the issue. The geometry of the bike itself may be a bit too steep for the technical terrain, though I could be wrong because it has more rear suspension travel than I would have thought. Bikes from the 90s tend to have odd setups, long stems and shallow headtube angles which mix for an interesting and nerve-wracking experience when you point it down the hill. But I could be wrong, this bike may not fit the stereotype.

I'm going to have soooo much to learn haha!

Yeah, but it's a whole lot of fun. I'm still learning myself, but I recently made the jump to full suspension after riding hardtails for quite a few years. I was able to pick up a 2005 Giant Trance that was only ridden 12 miles before I got it. It cost me 500, but if you're serious about this purchase it is almost worth waiting for a deal like that. If that Diamondback was like 150 I would say jump on it. But it is just old enough, and just expensive enough to make it a questionable decision. You could always offer less than hes asking if it is really something you want.

If you want cheap, get a hard-tail with v-brakes. If you buy cheap disc brakes and cheap suspension, you are just getting junk. You'll get a much better bike for your money if you drop the parts that are only good when you pay for quality.

If you go the hard-tail route, you could eventually add on a cane-creek thud-buster seat post if you just want a little extra shock absorption on pavement and gravel. They aren't cheap, but they are a much better approach than a cheap rear shock in my opinion.