This ALL depends on your clients needs. What will they want to deliver? What are they required to deliver? HDCAM is a standard delivery format, as is D5. HDCAM is cheaper than D5, so might be the way to go if you are just starting out. But even then, HDCAM is EXPENSIVE. D5, twice as much.
DVCPRO HD is a standard acquisition format, but not so much delivery. BUT, as I said, depends on who you are delivering to.
Shane