Dropping off a rental car in Munich
 

The morning after I arrive at my hotel in Unterschleißheim, Germany, I'll need to return my Enterprise car.

These are the possible return locations. How hard is it to drive into Munich at around 9:30 am on a Friday? Would I be better off to drop off in Dachau and take a 40 min train ride to central Munich or save the train fare and drive all the way to central Munich. Also if I drive all the way to central munich which of the below locations would be easiest?

Enterprise locations:

Schleißheimer, Dachau
or
in Munich:
Aidenbachstrasse
Kreillerstrasse
Landsbergerstrasse
Bremerstrasse

Unterschleißheim is about 10miles from Munich airport. You could easily drop of there and take the S-bahn into Munich.

Where do you need or want to go afterwards?

Theoretically, the airport would be an easy drop-off location. But the time you save for driving against the major flow of traffic will probably be eaten up by longer drop-off procedure at the airport (weekends can be really busy), and the 45 min ride back into town at €11.
It could be interesting, though, if you were departing later than day by plane as you could already check your bags (depends on airline).

The drive to Dachau will not be that much better than driving towards Munich city center as also the tangential thoroughfares see lots of traffic.

If you want to be in downtown Munich afterwards, the location at Bremer Str. is the best compromise. You may get a bit of traffic on B13 to get there, but 9:30 is more the end of the morning rush hour, so it should not be that bad. In addition, you'll return at a small location which should save time. Plus you have the subway nearby which just needs 15mins or so to the city center and runs much more frequently than the S-Bahn from the airport. And is already in the downtown fare zone which is less than €3.

All of the other locations make no sense.

The last weekend of Oktoberfest will make the airport even more busy.
Check routes from your hotel in Oberschleissheim to the Enterprise location at Bremer Str. before you take off.
It will either be A92 / A99 / B13 or B13 all the way. Google maps will calculate that pretty precisely with current traffic situation.
Dont't go A92 / A9 / Frankfurter Ring - which Google maps will show as the fastest option when there is no traffic at all (like right now).
But avoid that latter route on that Friday.

Good info, thanks!

I found driving in Munich to be easy, even with a 7 seater minivan. I picked it up from one of Sixt's central places and managed to find my way to our AirBnB just by recalling my journey on foot and guesswork. On the whole drivers in Germany are courteous and there is none of the haphazard anarchy one would witness in say Rome, Nice or Athens for example.

True, but Germans are hot on priority (Vorfahrt) and expect you to stop/give away. Won't slow down if they have priority. So watch the signs/signals assiduously and obey. And lane discipline. Almost every lane has its own filter sign.

Nothing wrong with that, that's how driving should be.

But that's not how people normally drive in UK, or how roads are planned and organised in UK.

We completed our trip. Using google maps navigator, the drive from the Unterschleissheim to Bremer Str. was a breeze. From there it was an easy walk to the U Bahn. Thanks for this good piece of advice.

You have bad driving in big cities anywhere, Munich included. Recently I took a taxi in Frankfurt and the driver was like a maniac, swapping lanes and overtaking on the inside. But generally speaking, away from big cities, German drivers keep to the rules and expect others to do the same.