Better to buy a property or buy a hostel?

Any of those options could be the best. It all depends on the circumstances for each specific case. In some cases, starting from scratch could be best; in other cases, buying an existing hostel could be best, or anything in between. There is no universal answer.

Your will have to perform the financial analyses for the cases that interest you, analyze different scenarios, and decide which one best fits your interests and your possibilities (investment size, expected profit, time of implementation, required expertise, etc.). But it is very improbable that one single project will have all the attributes of being the one requiring less investment, be the most profitable, be the fastest and easy to implement, and require the less expertise to implement.