If your family mostly comes from London, Gloucestershire or West Yorkshire, for example, then you may want to consider signing up to Ancestry, but if your family came from Kent, Devonshire or Leicestershire then Findmypast might be more suitable.
Many family history websites have agreements to digitise records such as parish registers and workhouse records from county archives, so it's worth checking to see which website covers the areas you're interested in. If your family mostly comes from London, Gloucestershire or West Yorkshire, for example, then you may want to consider signing up to Ancestry, but if your family came from Kent, Devonshire or Leicestershire then Findmypast might be more suitable.