My preference is for glass not polycarbonate but you will both views on here.

As Moon grower says, you will find that polycarbonate gets discoloured and is not very attractive after a year or two. However, it has much better insulation properties and would keep your greenhouse much warmer in winter. The downside is that it would let less light in at a time when you need maximum light.
In the UK there is special 'greenhouse glass' available which is a lot thinner than normal window glass.
I don't think it exists here, as when we arrived in France I went to a hardware shop and asked if they had glass for a greenhouse: 'verre pour une serre'. I was told it cost over 150 euros a square metre, which astounded me. I suggested I would use plastic or polycarbonate instead and the shopkeeper thought I was mad.
I then discovered he thought I'd said 'verre pour un insert' which is a glass fronted wood burning fireplace!
Ah, the difficulties of a foreign language!

Guest, the answer to your question depends on a lot of variables!
1) do you have children playing in the area where you want to place your greenhouse? Yes? don't buy "Greenhouse glass" as this breaks easily and is very dangerous. It breaks into large sharp pieces!
2) Can you afford safety glass? It is the best but is quite expensive!
3) If you have answered yes to (1) and no to (2) then buy poly-carbonate as it is quick and easy to replace if damaged by children and is cheap enough to be "throw-away". I used to deliver garden buildings for a living and the "greenhouse glass" was a real pain in the .......... If you get my meaning? ;~))