This might depend on the firms you want to target. Generally, Mannheim is the better schools as long as you write and speak German excellently. 

Hey guys ,
How would you compare these programs to the MBA from Saint Gallen ?
Cheers

According to the FT Global MBA ranking, they would rank like this:

1. WHU
2. St. Gallen
3. Mannheim

Salaries are overall very close. Comparing them like this belies the differences in placements and locations, though. St. Gallen is great if you are looking at the Swiss / European financial industry. 

The cost of living in Switzerland is very high compared to Germany. Discount the Swiss salary up to 50% to compare with Germany. https://www.numbeo.com/cost-of-living/compare_cities.jsp?country1=Germany&city1=Frankfurt&country2=Switzerland&city2=Zurich