> TikZ is more popular among mathematicians, mainly because it's more flexible and can do more.
John, I am surprised that you think TikZ is more powerful than xy-pic. TikZ is clearly more popular/active/... while xy-pic seems on it's way out.
However, the TikZ examples I have seen are way more verbose while still as cryptic as xy-pic.
TikZ examples I have seen laboriously specify all coordinates/dimensions/... in great detail whereas xy-pic also provides more advanced constructs like `\xymatrix` and particularly `\xygraph` allow high level layout descriptions and let xy-pic figure out the details.
If features like that exist in TikZ they were not used in examples that I have seen.
In programming terms TikZ feels like assembler to me while xy-pic at least feel like APL or Perl (unreadable for a reason).
However, I am just going by the examples I have seen, and the look of the TikZ code examples has discouraged me from investing the effort in learning it.
Maybe there is a more concise way to write TikZ that I have not seen yet.
I am still leaning towards haskell-diagrams. I do not know how well it works yet, but at least I like the concept. It tries to keep layout descriptions as high level as possible while being more readable at least compared to xy-pic :) and it also has low level hooks for when you need them.