If you choose Vajrakilaya as your yidam deity, it is very easy to progress on the path, since all obstacles are naturally dispelled and you can achieve the supreme siddhi without any fault.
"The practice of Vajrakilaya blazes at the very heart of the ancient Vajrayana traditions of Tibet. The wrathful heruka Vajrakilaya is a yidam deity who embodies the enlightened activity of all the buddhas, manifesting in an intensly wrathful yet compassionate form in order to subjugate the delusion and negativity that can arise as obstacles to the practice of Dharma. In fact, the practice of Vajrakilaya is famous in Tibetan Buddhism as an exceptionally powerful method to remove obstacles, destroy the forces hostile to compassion, and purify the spiritual pollution so prevalent in this age. -- Sogyal Rinpoche" ----- from The Practice of Vajrakilaya by Khenpo Namdrol
"On the Mahayana level, Vajrakilaya is the Bodhisattva Vajrapani, who promised to accompany any bodhisattva, like a shadow, from the path of accumulation up to the tenth bhumi. And for that bodhisattva, he would clear all obstacles and gather all favorable conditions necessary for progressing along the path. Vajrakilaya is none other than Vajrapani manifesting as a yidam heruka -- the one who clears away all hindrances on the path to enlightenment. Dilgo Khyentse Rinpoche" -----from The Practice of Vajrakilaya by Khenpo Namdrol