The only attributes steel poles bring are being incredibly strong and "cheap", on every other count they are much the less satisfactory than GRP/CRP ones. The weight saving alone is a massive plus for the composite plastic type.
Aluminium is the weakest of all.
Unless you are buying for extreme weather camping, leaving the awning on a seasonal pitch, or are desperate to save cost at any expense then IMO its best to go for the composite plastic poles. The moulded end fittings do crack from time to time over the years but are easy and cheap to replace.
Edit: sorry I cant get rid of a silly bit of code at the start.