The answer would be "on the level" but let's analyze why some athletes, even high-level ones, don't level the saddle. Let's start from the fact that, in addition to the set-up, the choice of model is important. Choosing the right saddle on the 1st attempt is difficult, if not impossible, a lottery: only experience will make us choose the best saddle or a careful analysis of the width of the ischial bones and their own biomechanics.

In a nutshell, everyone should evaluate the saddle best suited to their physique: be wary of anyone who recommends that saddle or the other.
BASIC RULES SETTING UP ON THE SADDLE
If this is your first setup, the saddle needs to be levelled. Even saddles like the SMP, with their curved shape, require a level saddle between the rear and the front (you can find all the details on the SMP website). In competitive riding, especially in Cross Country, there is a tendency to lower the tip slightly (in the order of 1/2°), nothing excessive.

LOWER THE TIP OF THE SADDLE
Why is the tip lowered? Because, on steep climbs, you have a more profitable position, without loading too much on the perianal area and being able to go to the tip of the saddle more easily. But don't overdo it: a saddle that is too low at the tip causes an excessive load on the core and iliopsoas muscles. This leads to more immediate power but also more fatigue, not to mention that, in the long run, it can cause inflammation, contractures and other problems. This set-up is also used for time trial road races, being short and requiring a lot of power in a short time.
If you lower the toe so much you have to do it with criteria but we recommend it only to professional athletes, trained to perfection and followed by specialists.


RAISE THE TIP OF THE SADDLE
Adjusting the saddle of the Mtb with the tip upwards is wrong, at least for the disciplines where you pedal, such as cross country, marathon or enduro (although the latter is a mix between pedaling and downhill). The high tip creates excessive pressure in the saddle pad with inflammation and numbness. Then, in the long run, you risk more serious damage. Other indirect problems are extra work for the lumbar muscles and overloading the back with an incorrect curve of the spine.

The saddle up is only used in DOWNHILL, where an upward saddle helps to always have it ready between the thighs in case of corrections. And then, if you are right, in downhill it only runs downhill so a toe up gets a fairly level position downhill on the steeps.
WHAT ABOUT THE ADVANCED SADDLE?
Modern biomechanical studies agree that a more advanced position than in the past gives greater benefits in terms of performance. But you must always trust the geometry of the frame: on some very vertical vertical tube frames (these are the modern trends, i.e. make the seat tube more and more vertical) it is not necessary to move the saddle completely forward but even in a central position you get to have the right biomechanical dimensions.

With some latest generation frames, it is therefore possible to obtain the correct positioning of the saddle without reaching extreme positions of the saddle, where the risk of breaking the hull is just around the corner. The main advantage of forward pedaling is a greater and more profitable push on the pedals, especially when going uphill. Contraindications: few but certainly there is a greater overload of the knee so exaggerating this position is not a good thing. And, in users with knee area problems, not recommended.
But too far back also causes problems such as back pain and excessive strain on the hamstrings (back of the leg).
HOW HIGH DOES THE SADDLE GO?
The right, simply. A saddle that is too high leads to an undulating movement of the pelvis and this is not good. A saddle that is too low places too much strain on the quads and is not a profitable position by not having the correct angles. You need to have a height that allows you to use the leg muscles correctly. For the more meticulous, in MTB there is a tendency to have the saddle slightly lower (especially in e-bikes) to better control the bike on uneven surfaces (we are talking in the order of 1-2mm).
To learn more about this last topic, I refer you to one of our specific articles: How to adjust the position in MTB: height and length
