How will you be using the HTPC? Streaming videos over the local network with Blu-ray/DVD rips? CableCard and/or OTA tuner? Online streaming? What software do you plan on using - 7MC, XBMC, J. River, or another? What HTPC hardware will you be using, including the A/V and display devices?
The answers to those questions will have an impact on which card is right for you, or will determine if a dedicated card is even required.