Do I buy 80% wool carpet, or the Polypropylene type?

[buzzer]

I need to do a few rooms in the house, a couple of bedrooms and the stairs and landing. I made the mistake about 5 years ago of buying a man made carpet, not sure what it was made of, but its crap. the pile on the stairs and the bedrooms is flat, it looks dirty and does not clean well.

I am told by the carpet salesman that the new type Polypropylene carpets are much better than the older man made stuff, and its about half the price of an 80% wool carpet, so not sure what to buy.... I am always sceptical on what the salesman tells me...

So anyone any comments and in particular experience about the new type of Polypropylene carpets?