I have opportnities to buy either Mercedes 15" x 6 1/2 steel rims, or
Audi 16" alloys for Cunegonde. Stock  suspension and a stock 1.9L with
stock 4 speed trans  50% street/50% unpaved back road driving with
moderate loads. Very little snow and ice, lots of rain driving.

Which rims will give me the greatest tire selection? My current stock
14"a with Michelin X truck tires have got to be replaced!

Thanks for all your sage advice.