New Valves

Ok if I am porting the heads my self (basicly making them nice and smooth), and are replacing the srings/locks/retainers for my cam swap, what are the advantages to changing the valves. Ive done some research on the manley valves, and I see they offer different designs. So what is the difference in going with aftermarket performance valves vs stock valves? Is it even worth it, unless your doing heavy porting? Or is mainly to lighten up the valve train?

If it is worth replacing the valves, what size and brand should I go with?

Also has anyone done a write up or does anyone have pics on the spots to clean up and polish when doing the porting on your own? Thanks guys.

Mike