“Which toothpaste is best for gum recession?”

Don't think toothpaste can treat gum recession. You can see a periodontist to do a root coverage procedure to reverse the recession if you don't have periodontal disease. more info in the video below:
https://youtu.be/kw2wkNP-s_8

Gum recession can be caused by brushing hard with abrasive brushes.  Try to stay away from toothpaste that has an abrasive component like most whitening toothpaste.  If you have sensitivity due to gum recession, you can use toothpaste with Stannous Fluoride and/or Sodium Fluoride as active ingredients.  The best way to determine the best toothpaste for you is to visit your dentist and they will recommend the best that suits your condition.

Gum recession has a tendency to create tooth sensitivity. I recommend Sensodyne due to small abrasive particles and potassium nitrate to relieve sensitivity. Ask your dentist or hygienist for brushing tips with gum recession and always use a soft toothbrush.