Keen mountain bike riders have many types of bikes to choose from. Nowadays all good bikes have good front suspension good disc brakes and good gear systems, and the decision comes down to whether to have rear suspension, rear gears only, fat tyres and a seat dropper for steep downhill sections.
For the hobbyist mountain biker who really wants to just stay fit and be able to get out into the Hills and rough tracks, a hardtail bike with fat tires and rear gears can be a great solution. And if the biker is older and a bit more timid then a seat dropper can be a perfect addition for those slightly scary downhill bits.
The real advantage of fat tires is that they have a much better surface area and much better grip, and they generally feel a lot safer over rough terrain then the thinner tires do. This is especially so in the wet, and the rider feels much more secure both going uphill and down hill and slippery tracks.
The bikes are a lot of fun or level but rough tracks, and the fat tires give the biker a sense of riding a very light dirt bike but with pedals instead of a motor. The rider can maintain a high speed over rough terrain, although they need to stand on the pedals often when going across potholes in order to absorb the shocks to the back wheel and stop the bike bouncing. It can take a bit of getting used to, particularly if the rider as previously accustomed to a good rear suspension, but the extra lightness of the bike can easily make up for this small disadvantage. Fat tires can be pumped as high as 20 psi, but over rough and slippery tracks are best at 12 to 15 PSI. Riders will probably pump their tires up to 20 psi during a dry summer months, as this means the bike will go even faster over rough tracks, which can be a lot of fun.
A hardtail modern mountain bike can be a very good cost-effective solution, as the disadvantage of not having rear suspension is made up for by the extra lightness of the bike. A hardtail is obviously not suitable for high speed rugged downhill racing, but for the amateur rider looking for a safe and economic and fun way to get out of the hills a good hardtail can be a great solution.