I have enjoyed reading the openings of both books and there are strong arguments for both being the best. Both of the books open with attention grabbing sentences. In the text Skellig you immediately want to know who or what has been found in the garage. It states : I found him in the garage on a Sunday afternoon. The use of the pronoun him keeps the sense of mystery about who or what was found.
In the text Kensuke's Kingdom there is also an attention grabbing opening sentence and I really would like to know why Michael had disappeared and what had happened to him on his twelfth birthday. I also would really like to know more about who Kensuke was and why he was such ' a good man.'
However I think I prefer the opening of Skellig as I am very intrigued by what will make Skellig a creature like none other in the entire world.