The straight AC welder switches polarity 120 times a second, so cable position isn't an issue. Yes, the DC machines have a definite polarity preference for some types of rod. For instance, 7018 is a reverse-polarity rod used to make a smooth cap pass during pipe welding. The root pass was done with 6010 rod, which made an ugly, splattery weld that didn't need much slag removal, then the cap pass was done with reverse-polarity 7018 to give a smooth, high-strength finished surface.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!