Consider its safety and reliability. Almost all bikes of this type are now equipped with suspensions. They are necessary to absorb vibrations and shocks due to rough terrain.
The telescopic fork offers a true mountain bike ride comfort, very valuable especially when hiking last long . Some bikes sometimes integrate additional suspension in their context (this is called a “full suspension bike”).
For the frame, steel remains the material more affordable financially. It is comfortable and executives are performing.
Aluminium is both light and strong.
The carbon and composite materials are reserved to performance.
Finally titanium is the ideal material: soft, stainless and very strong. Disadvantage: it is very expensive!
Generally, manufacturers indicate the size of their frames in inches (1 inch = 2.54 cm). This corresponds to the length between the top of the tube under the seat and the bottom bracket. Basically: your crotch length.
The best way to choose is to test and compare several models to know what size bike pass. Once seated on the saddle, if you touch the ground tiptoe is that the bicycle is suitable for your size.