Camping is good in the summer month. it is cheaper than hostels.
But the camping areas are often outside of the cities, so you always have to take a train/metro/subway to come in the centre of the city (which costs extra).
Also you do not have lockers there to place your money, passports, etc ...
And you have always transport a tent with you (more weight).
Hostels are more expensive than to camp. but more comfortable, in the centre of a city, there are lockers ...
So my experience is: in big cities like Paris, London, Roma, ... I prefer hostels.
In small cities or on the country side, when go to beaches, I always do camping.
And when I am doing transfers from one to an other country, I use night-trains.
A good mix of all ...
for hostels have a look on rail.shop/hostelworld