If you are going stock I'd reccommend the Chevy Duty harness. It has all the wires cut to length, terminals installed and sockets for the dash bulbs.
If you are building a custom I'd go with the painless. I looked at them at a distributor's display at the swapmeet last weekend. I was very impressed. They come with a modern style fuse box complete with fuses and flasher, in either 12 or 18 curcuit. Of course being for custom installations you have to cut the wires to length and crimp your terminals. The sales guy said there's usually plenty of leftover wire.
