Well, first of all I think we need to realize that the impression of harsh or soft or sexy is always subjective to a certain degree. Some attributes of spoken languages might be easier to measure than others, for example an attribute like melodic (we could measure the distance between lower and upper frequency). Italian is quite melodic for example.
Now about the German accents. There are many. The list includes the following at least:
Ripuarian, Moselle Franconian, Central Hessian, East Hessian, North Hessian, Thuringian, North Upper Saxon, Rhine Franconian, Swabian, Alsatian, Lorraine Franconian, Silesian German, High Prussian, Lausitzisch-Neumärkisch, Upper Saxon, Bernese, Walser German, Oberpfalz Bavarian, Lower Bavarian, Higher Bavarian, Northern Austro-Bavarian, Central Austro-Bavarian, Northern Austro-Bavarian, Cimbrian, Hutterite, Low Alemannic, Central Alemannic, High Alemannic.
The best map is only available in German, but it’s still worth taking a look at:
http://de.wikipedia.org/w/index.php?title=Datei:Deutsche_Dialekte.PNG
Some are very soft such as the Austro-Bavarian dialect spoken in Vienna or Moselle Franconian spoken in the Trier area or Swabian spoken in the Stuttgart area. In Swabian all sp and st endings are replaced by softer sh-p and sh-t endings. If sp and st qualifies as being harsh then High German spoken on tv and in the Hannover area could be considered harsh. Personally I don’t think sp and st sounds harsh, though it’s less soft than sh-p and sh-t for example.
Directors of older Hollywood movies never bothered to check with native speakers before release and when watching them in English the German parts sound like very unprofessional filmmaking. This changed in the 70s. And almost all top Hollywood movies from the 80s and later use correct German. When dubbed into German more attention can be paid to the correct slightly accented High German the real character was using. Hitler was born and raised in Austria for example. Later on outside of Austria he had to speak High German otherwise most people from Hamburg or Berlin would not have been able to understand him. But a slight touch of the Austrian dialect remained.
Today in the big cities dialects are on the retreat. Only 30% of Munich’s population is actually from Munich or its surroundings. You will find people from all over Germany moving there, and not only that, lots of Europeans and people from other continents too. At work High German or English is the standard language.
Let’s see how many German accents do survive. Some have already gone extinct over the past decades. But the same can be said for the UK or France. Globalization is one of the key drivers.