A seperate fridge and freezer is by far the best solution for most households, because a seperate freezer will have a much larger freezer compartment and can be placed in a shed or garage freeing up valuable space in a kitchen.
The only decent efficient freezers are chest freezers with a lift-up lid, these freezers are the most efficient because cold air is very heavy and when you lift the lid, the cold ( frozen air ) remains within the chest freezer. With upright freezers, when you open the door the cold ( frozen air ) tumbles out of the freezer onto the floor, to be replaced by warm moist air ( thus leading to the freezer frosting up and requiring to be de-frosted, it also requires the compressor to work for longer to cool this extra warm air that has entered the upright freezer.
Modern upright freezers have tried to overcome this drawback by having enclosed shelves to keep the cold air in when the door is opened but this simply reduces the useable space inside the upright freezer.
If you look into Iceland or other frozen food stores you'll notice that the majority use chest freezers . Even if customers in these stores leave the lid up, these freezers are very efficient because the cold air being heavy stay surrounding the frozen food stopping it from de-frosting.
To gain most efficiency from a chest freezer wire baskets should be used to hold the foods and all contents should be marked so that it can be found quickly and easily.
Unfortunately most people don't have huge kitchens that can hold a chest freezer, so a shed or garage is the best place for them.
Big posey fridge/freezers and integral fridge/freezers look
good, cost the earth and are not efficient, however some people these days go purely on looks. One day I hope they learn to judge something by what it does and not by the fact that it looks good but is useless in the real world.