Actually I like Munich better than Salzburg but only because while beautiful, Salzburg is very, very touristy.
I disagree; well, in part. I love Salzburg and yes, it does get a lot of tourists, but I would never consider it "touristy." To me, that's a place where you are stumbling over huskers at every turn, and every other shop sells cheap souvenirs. Salzburg is crowded, yes, but very beautiful and you will not regret visiting there.
I do agree with the others that you should take the train and not drive. It's difficult to find parking there, and it's very easy to get around using public transport. You can get an early train and be there in about 90 minutes. It's around a 20 minute walk to from the train station to the city center, and since you're there on a day trip, you shouldn't have any luggage to weigh you down. And of course, you can always get a taxi into town.