What should I look for in a Processor??

What type of coding is neccesary?? Do i need every dolby, thx, etc. which settings or features are most important. I am thinking about purchasing a used one and it appears some have component video switching, not sure how many are HDTV cable through this switching due to their age. I could very easily just run the video directly to the tv if this is a problem.

thanks for the help..