The Lamrim (p.252-253)says: "THE GURU IS MUCH KINDER THAN ALL THE BUDDHAS "
"75000 buddhas, another 76000 buddhas, yet another 77000 buddhas and so on, came into the world solely to be the object of Buddha our Teacher's build-up of accumulations. Moreover, in this eon alone, the buddhas Krakuchchanda, Kanakamuni,, Kashyapa, and so on, have guided boundless numbers of disciples, but they could not subdue us. THE GURU IS TEACHING THE COMPLETE AND UNMISTAKEN PATH NOW - EVEN THE PREVIOUS MANIFESTATIONS OF THE BUDDHAS COULD NOT DO BETTER. Thus although the guru and the buddhas are equals in terms of good qualities, the guru is THEIR SUPERIOR IN TERMS OF KINDNESS.
Geshe Potowa said that the guru is like someone who gives a dying person food during a famine, while the buddhas are like those who give slabs of food in times of plenty.
Now that we are deprived of Dharma, the guru teaches us the same Dharma, so he is more compassionate".
Therefore, we can safely conclude that the guru is the kindest of all, because he is the one to teach us the Dharma, which, (as in the form of the Lamrim), presents us with the path that lead us out of suffering, through subduing our minds, and on to enlightenment.
Therefore, we should properly rely on him by devoting ourselves to him as our spiritual guide.
Thus, we see this in the prayer 'Yonten Shigyurma' :
"Well realizing that the root of the path,
The foundation of every realization,
Is to properly rely on my kind Gurus,
Bless me to do so with great effort and devotion".