At first glance, I didn’t realize the cups and pipes had different kinds of connectors. We can easily rule out all of the cups that are underneath blocked pipes. That means 4, 5, and 6 are out of the running right off the bat. Cup 7 doesn’t have a stopped pipe, but it has a hole in it. In any scenario where we could pour fast enough to overwhelm the leak, the cups above 7 would fill up faster.
So we’re left with just 1, 2, and 3. But 2 has the same logical loop as cup 7, where a pour big enough to fill it, despite its outflowing pipe, would still fill cup 1 first. Otherwise, any normal pour would flow out through the bottom, 7 would never fill, and 2 would never fill either.
That leaves just 1 and 3. But 1 will always be spilling water through cups 2 and 7, which means it won’t ever be filled under normal circumstances. If you look at cup 3, it’s the only cup that has a fully closed surrounding; both pipes that lead outward are closed.