mig will be the easiest to learn. arc welding is also nice to learn though. if you can practice on your grandpa's welder, why don't you get a mig to practice that at your place, then you can practice arc at your grandpa's place.
oh yeah....DO NOT BUY A HARBOR FREIGHT WELDER
spend the money and get a decent miller or lincoln
oh yeah....DO NOT BUY A HARBOR FREIGHT WELDER
spend the money and get a decent miller or lincoln