Nothing can beat a hardtail for flat-out climbing speed and efficiency, but they suffer on the technical features found on modern cross country courses.

Why are hardtails better?

It will make you smoother - If you don't learn how to float your bike over roots and rocks, a hardtail will either bounce you off the trail or rattle your teeth out. ... Also, due to the lack of rear suspension, bunnyhops are quicker, it's easier to pick up the front wheel, and the bike is generally lighter and nimbler.

Is a hardtail faster than full suspension?

Speed When It Counts: The aforementioned traction and handling chops that a full-suspension bike possesses mean that on certain racecourses, a full-suspension bike will be faster than a hardtail bike, despite being heavier with slightly less efficient pedaling.