I choose Construct 3 because:
The event sheet editor
Lol there's other reasons too but it could be argued that Gdevelop have similar aspects.
I like how close Scirra interacts with the community and I do think they are very passionate and knowledgeable.
I like the multiplayer plugin, which for some reason gets a lot of hate, but it works extremely well and easy to use.
I like the way construct 3 feels UI-wise and the structure.
Performance comparisons would be interesting, but I wouldn't have expected too much difference between construct 3 and gdevelop, maybe in certain areas but there'd be a more dramatic different when comparing one of these engines to something else. Scirra have had an opportunity to reinvent their runtime engine after making construct 2, so I assume they have designed construct 3 with performance and efficiency as top priority.