Option 3 because the large numbers help even out the weight more. The numbers also look like they're coming in/out of the pipes. The only thing I don't like is that the numbers don't actually look like liquid, but I'm not into typography so I wouldn't know how to make them look like it.
3. Because the angled letters look like they're rising out of the pipe, not sitting on them. They look like numeric fluid overflowing. IT fits better, and the drop you have on the C fits well with them. Copper is easily bent. Having worked with copper plumbing before, the off kilter #'s fit better with my experience of the metal. I have not yet seen a perfectly aligned set of copper pipes. NOT EVER.... but that's possibly due to knowing a lot of less symmetry obsessed plumbers.
2nd - 2. The numbers look solid, fixed, and not at all like part of the design. They look tacked on.
1. - #'s too small, and again look like they don't belong.