I don't use any pressing agent very often, but sometimes it's necessary. From my experience, Best Press helps to take care of the wrinkles, but Magic Sizing makes the fabric much stiffer. I used Sizing when I was working with very long bias edges to help keep things from stretching. I don't think it's necessary for normal cuts.

I've only used Best Press. I love it when dealing with HSTs. Some of scents make me sneeze, tho. Linen is the biggest culprit. I love the Caribbean Beach scent. It doesn't gunk up my iron at all.

I use the Vodka Press mostly. It smoothes any wrinkles and presses seams nicely. I like a Sizing for blocks with diagonal seams to keep everything firm and square (if I sewed right).