Mel has pretty much summed it up although I will disagree one point. If you take Bradcot, Dorema and Isabella full awnings, there is virtually no difference in weight, and an Isabella Capri or Ambassador is classed as a touring awning just as are the offerings from Bradcot and Dorema. The description heavy duty I would replace with quality, but you pay for this as in any other item. All three companies also do a heavier type awning, i.e. an all season awning or an awning suitable for a seasonal pitch.
There are other makes of course but in full awnings, thats the main three as I see it. There are lightweight awnings of varying quality, but I would suggest if you are going for a full awning, get a proper one. The other option as has been mentioned is a porch awning. Again these come in varying sizes and quality. One thing that is often mentioned with porches is that the way they sit against the van, very often one side will half cover a window, and a lot of people dont like that.
Once you have decided on either a full or porch, there are other things to consider. The poles. You can opt for aluminium, light and weak, steel, heavy and strong, or carbon fibre, light and very strong. There are also air beam awnings, no poles, just inflatable beams.
If I were you, I would have a look at my nearest large caravan dealer who are likely to have a good display of all types of awning. Take your time and get it right, its an expensive purchase.
If asked about personal preference, I have in the past always had a full awning. I bought one of the better air awnings and used it once. I personally hated it and immediately got rid of it and went back to a full awning. My preference is the Isabella, I have had four of them now and they have all been superb.