Sorry, first day should be start from Stuttgart - Metzingen - Bad Urach - Schloss Lichtenstein - Burg Hohenzollern -... (somewhere to overnight?? any advice)

If the next day (2nd day) i would like to go (Schiltach),Schwarzwaelder Freilichtmuseum Vogtsbauernof (Gutach), Gengenbach and return to stuttgart. Is it possible? Please advice me some scenic road along the way to stuttgart.

Third day, visit mercedez-benz museum and some interesting place in stuttgart before send car back on 14:00

I think that it is possible to visit all the places (Metzingen, Bad Urach, Schloss Lichtenstein and Burg Hohenzollern in one day, however I think that is quite unrealistic. First, the outlet centers in Metzingen are scattered all over the city so it probably is at least a half day of shopping unless you restrict yourself to one or two. You could certainly have a quick look at Bad Urach in less than an hour, but if you want to visit the palace, the old castle ruins or the waterfall, certainly much longer. Schloss Lichtenstein is east of Reutlingen necessitating passing through this city with heavy traffic so it is slow or a detour through the mountains which will also be slow. After you leave Reutlingen than you could then head toward Tuebingen and pick up Hwy 27 which is a freeway most of the way to Hechingen where Burg Hohenzollern is. of course, if you do castle tours (may be only available in German, but they give you a written text to look at), then this will take a while too.

Personally, I would skip Bad Urach, it's a pleasant town in a mountain valley, and stop in the lovely old college town of Tuebingen on the way to Burg Hohenzollern, and the medieval monastery Bebenhausen is well preserved and just to it north.

Personally, I'd try something like visit Metzingen, then Bad Urach, see Germany's oldest state stables at Marbach (Gomadingen), then visit Lichtenstein Castle. That will probably already have shot the day, so return to Stuttgart. The next day visit Burg Hohenzollern first, then return to Tuebingen, see the old town, and visit Bebenhausen. Take the backroad to Stuttgart which will pass through Waldenbuch which has the Ritter SPORT chocolate factory. Visit their museum with art in the form of squares, their small chocolate museum if desired, and also their sales room for discounted candy, then return to Stuttgart.

The interior of the two castles aren't really comparable, let's just say their different. Burg Hohenzollern is historically significant as it is the family seat of the once influential powerful Prussian Hohenzollern family, German Kings and Emporers.

You probably do not need to drive to the Mercedes Museum, just use public transport.

I know this omits the Black Forest, but its the furthest places away from Stuttgart, and the other places I've mentioned are excellent too.

What I've suggested is more or less what we show to foreign visitors, leaving out Metzingen.

If you decide to pursue your Black Forest visit, you might like to overnight in the very pleasant town of Rottweil which will be between Hechingen and the Black Forest.

Marcopolko! Ich moechte Ihnen fuer Antwort ein herzliches Dankeschoen sagen. :)