On the top of the Basilica St Peter
That vatican is impressive, imposing and outstanding nobody has no doubt of it. not matter from where you look in Rome you will see the dome of the Basilica St Peter on the famous St peter's Square.
I don't know how many time I had been at the vatican, but for the very first time I went on the top of the dome of the Basilica St Peter. For sure is one of the best view of the city. From there you can see almost all Rome and also the Vatican City.
If you are on limit budget and don't want to pay for guides and the tour on the Vatican museum, I really recommend you after had visited the Basilica St Peter, with 10 euros, you can visit the top of the dome of the Basilica St Peter.
You can pay 8 euros to get to the top of the dome but you must climb all the steps and I don't really recommend you pay 8 euros. 10 euros you go by elevator till a almost of the top the dome, where you still have a few more steps to climb.
If you are not in good shape, it definitely is not for you.
Take a private photography tour around Rome and travel with a local professional photographer.
Make your reservation in advance.