I have a 68 w/sbc 4-speed,p/s and I would like to find what would be the
the best choice for exaust?

headers, no doubt

Headers would be the way to go to free up 20 horsepower or so!....Think of exhaust manifolds as corks, which would not make the motor breathe freely!.....Just keeep in mind, running headers, you'll hear slight ticking noise coming from the tubes near the cylinder heads, this is the tick of the exhaust flames hitting the tubes inside the headers!....It may not even be that noticable!

Originality, or added cost of headers, would be the only reason I could think of to keep the manifolds. Otherwise I can't think of another reason not to go with headers, IMHO.

If you are keeping the engine stock, then keep the exhaust manifolds. They are more trouble free, no blown collector gaskets, no header to head leak, no loose bolts etc. If you don't keep the engine stock, you will want it to breathe easier and get more power with headers.

what brand headers fit the best and dont burn up the starter and p/s box ?

Best fitting ? probably Doug's D368 or a set of Lemon's headers.

Most economical ? With 307/327 Frame mounts use Dynomax or Summit brand.
.........................With 302/350 Frame mounts use Hooker Competition headers.