for heat distribution I'd lean towards copper or brass (they heat up fairly quickly). but the fact they're copper or have copper in them would be the reason i'd veer away from them too. brass will take longer to heat up but should hold the heat for longer then straight copper.
Should be right running tubing around them provided the tubing doesn't melt from the heat generated (thats if you're planning on using plastic, and if it should get that high).
Anyone know if titanium leeches anything into the water? that would be the next option I'd pick but thats pretty pricey . can just run the water thru the pipe, under the light, then back to the tank if it doesn't leech.