Personally I prefer Brother over Bernina. No experience with a Janome but hear great things about them. My advice is go to the different dealers & try out their used machines in all the brands-very good chance with your budget you'll get a much better used machine than a new machine in that price range. Many dealers will also give a 6 mo or 1 year warrenty with a used machine.
So many new machines come on the market with more bells & whistles so older very good machines get traded in for the newest machine, which could mean a good deal for you.