Be glad it's not the SCP statue thing
Get the Doctor, Slye, and Erin. We're fucked if you don't.
but then again... hmm it is a good point good thinking but I no think I want to die bye Slenderman and Mr/Ms./Miss/Mrs. weeping angel, it'd be someones personal hell on Earth
ITS AN IMPOSSIBLE CHOICE.
Not really, unlike Slenderman, Weeping Angels have a clearly understood motive: To feed and survive (Considering the fact that the Weeping Angels don't even kill you in the physical sense)
Plus, they have a sentient intelligence, since they can "communicate" with humans. (Which requires them to kill someone in the physical sense, which may have been inspired by SCP-173, since the SCP originated before Dr. Who)
Slenderman doesn't have a motive, in truth, he doesn't even exist within our dimension.
Of course, that's if you believe in the logic behind Slenderman. (Google "Tulpa Effect" for more information)
I think it would be more of a hostile confrontation between these two like the one that already exists between HABIT and Slenderman.
Also, Slenderman can move on his own, he simply chooses when and where to do so, unlike the Weeping Angels who are permanently frozen as long as someone looks at them.
That makes you wonder: What if Slenderman stares at a Weeping Angel?