Well, that is impossible. I love them - the 3 amigos are the best and my favorite guitarists ever !
Dave and Adrian always will be the perfect guitar duo, but Janick is so underrated as a guitarist and maybe as a composer too - he fits Maiden and the unique style of the band perfectly. Besides, he wrote a metal masterpiece like Dance Of Death.
Janick is my favourite but I don't think he's necessarily the best - there are so many levels and criteria with which to measure "good" and they all score points for different aspects. But I do think he brought something to Maiden that they never had before, and I do think that Dave and Adrian have been affected positively by Janick's presence and contribution.
I think the main point is that Maiden needs all three of them. They are the perfect team .
Adrian these days, but Dave if you look at Maiden's entire career. For me, he is THE Maiden guitarist. Not just because he has been on all of the albums, but I feel like his style is what I most associate with Maiden's sound. And of course his smiling and how it looks so easy when he plays helps.