both! as a combo knitter, i have learned to work a stitch as it lies.
on flat knitting (rows) this very often means i knit into the back of knit stitches, but the front of purls.
in the round, the opposite!
after tinking or frogging, how ever the stitch lies.
Combo knitting is physically easier to do (and do evenly) but requires you understand how to work a stitch with out unintentionally twisting it. (it requires more thought! at least at first.)
it also requires some accomidations for decreases (since these need to be reversed on flat knitting, (but not when working in the round--unless you are decreasing purls!)
LOTS OF THINGS TO THINK ABOUT! but once you grok knitting, you can do these things almost with out thinking.. and faster if you work in the Combo method.