I used to use the all in one rain suit and honestly don't rate them they are brilliant if you can keep the neck done up if not they are pointless, my problem with it was my 19in neck and it just wouldn't do up in the end I resorted to using gaffa tape to get it to close around my neck.....and yes I looked like a Michelin man.....not a good look.
2 piece is the way to go imho