Went thru a thread like this for UT2003 (because there's very few things in life I like more than ChaosCTF - well, that and letting my opinion be known ), and I'm happy to brag that my #1 choice was also the highest rated CTF map in Phase 1 of MSUC. (3rd overall behind 2 DMs)
And now, Plutonic has made the same map available for UT2004.
<a href="http://www.planetunreal.com/plutonic/" target="_blank">Unearthed City SE</a>
No better place to start for UT2004. Thank you Plutonic.