Every coin has two sides. Being a hostel resident I have come across a lot of good and bad times during my brief hostel life.
PROS : 1. The hostel has staff appointed by it to make sure that it is clean and well maintained. 2. You get food and meals daily at fixed times with none of the days being skipped. So our diet is not affected. 3. Round the clock security is provided by the hostel to its residents. So parents don't have to worry about it. 4. There are a lot of people of similar age around you. You don't find yourself feeling lonely. With friends around you, a case of homesickness does not arise. 5. Most hostels are also a collection of students pursuing the same stream of education. Thus, it is a perfect environment for crowdsourcing. It provides a perfect environment for group studies with the easy availability of notes and presentations, a list of potential questions, faster doubt clarification. Night outs are no longer a big deal. You could keep each other awake and discuss all that you need to study. Exams have never felt easier.
CONS : 1. Your hostel roommate is like a surprise gift. You may or may not like it. It is great if you have similar interests but sometimes the differences can make it difficult to adjust. 2. Hostels have their own politics which needs a very tactful mind to deal with. 3. Your freedom is restricted. There are a lot of rules that you have to follow. Your hostel might have rules where you need to make entries whenever you enter and exit a hostel. You would be needed to get back to the hostel before a certain time in the evening. 4. You are sharing a bathroom with a lot of people. There might be issues with sanitation and hygiene with so many people. Besides, mornings can be at times a test of your patience. 5. There is no privacy in the hostels.
PG accommodations are very different from the hostels. The rules in PGs are much more relaxed than in hostels. You get a lot more independence and freedom. But PGs might not offer any security service. There are fewer people staying in a PG. They could be of different ages pursuing different things. Some of them might be students while someone else would be working. A mess facility might not come with a PG accommodation. You might have to get a tiffin service or it would be provided by the PG owner. A PG might not have some of the advantages that a hostel has. But it offers a lot of other things in exchange for this. In the end it your selection would depend on your personal preference.