Beef stock is what I have gone with. You can opt for Lamb stock if it is available. If neither of the above is available, Chicken stock would work too. The best in terms of imparting flavour would be lamb stock or beef stock. It would be great if you can make beef/lamb stock at home but it takes a lot of time mind you.  When it comes to buying beef stock, make sure that the stock is not made of artificial flavors and so get one from a well-trusted brand. Many brands do not go for the long-simmering process of making stock by breaking down joints/cartilage and go for artificial flavors. If you are not sure, a chicken stock made at home from scratch or one from the store would be fine, as chicken stock is not that difficult to make so brands would be honest at that.