What's best product to do final skim coat drywall mud? How wide is good to feather nice when sanding? 1 foot?

I like usg lightweight for the final coat..how far you pull the joints out depends on how well and level the framing is and how proper the drywall in it is...there are more than 2 types of joints as suggested here..there are joints which are the ones that are up and down..and 4 feet long..there are then long joints..which are the ones that run the length..then there are angle joints(all corners)..then there are header joints..the small ones over the doors windows etc...a good job on the framing a 12 inch float will be sufficient..but I have had som e joints that I had to float out almost 48 inches due to bad framing..so there is no set formula on how wide to pull the joints, this all depends on the framing and drywall job done prior to it..