Reddit reviews Diamondback Bicycles Sorrento Hard Tail Complete Mountain Bike

>I will be doing it more for cardio on local hiking trails and such, light terrain. With that said, i would want something decent that can be upgraded If I get more serious and want to start hitting legit parks and trails.

At your price point you're not looking at a bike worth upgrading in any serious capacity. Tires/grips/saddle would be the extent of the upgrades I'd recommend. For example, the Sorrento listed here has rim brakes, a jank drivetrain, and a pogo-stick fork. Assuming you can find used parts to replace all of those, you're still looking at $300-$400 of upgrades, (assuming the bike has standoffs for disc brakes), and you're still riding a bike that's nowhere near as good as say, a Raleigh Tokul 3.

If you're buying a bike to try out MTB without spending a ton of money before buying a new, better bike, the Sorrento is great for that. If you're looking to buy a bike that you can upgrade and keep riding for years, the Sorrento is going to come up a bit short, and you should consider spending a bit more money on a new bike or checking out PinkBike.com's Buy/Sell page for a used bike.

I recommend the Tokul because it's relatively cheap for what you're getting; a 27.5+ (The + is for fatter tires) hardtail with a quality entry level fork, a 1x11 drivetrain, modern geometry, and disc brakes. Personally the only thing I'd upgrade on that bike is the brakes, but that's more a personal preference since I'm heavy and ride like an asshole.