This is a question many of us who are moving house ask ourselves. However there is no correct answer. It all depends on how much stuff you have to move. If you are living in a flatting or house share situation and don't have an entire house load of furniture, then hiring 2 movers should suffice. If you have a full house load of furniture and 3-4 bedrooms then hiring 3 or more is going to be a better option for you.
Hiring 2 movers may seem lower on cost but this also mean the movers will move slower so there is the possibility that the move may take longer than anticipated, which in turn will cost you more money. There is the option of hiring 2 movers and getting a couple of burly mates to help lift the heavier furniture out to the truck.
Hiring 3 movers is always going to make the move faster and this way, you have 1 mover stay in the truck to pack the contents efficiently while the other 2 move the furniture. Having 3 movers is always going to make things go quicker for all involved, so if time is of the essence, you will want to consider hiring 3 movers.