We will be attending a conference in Mainz in June, 2019. Either before, or after the conference we would like to tour Munich, Salzburg, Hallstatt and Vienna. Should we rent a car or take trains? If trains, what type of pass? We would like to visit Neuschwanstein, also Melk Abbey, and do some hiking. We are thinking a couple of weeks total, will that be enough time considering 3 nights at conference? I'm thinking we would fly into Frankfurt and out of Vienna (or reverse). I don't like hot weather...would it make any difference weather wise if we did conference or touring first? Thanks in advance!
Why do you think you need a pass? A pass is wholly unnecessary. Buy a Bayern ticket (Deutschland Bahn) to get you from Munich to Salzburg. Use an Einfach-Raus ticket (OeBB) for you Hallstatt visit. Buy a Westbahn train ticket for Salzburg to Vienna.
There's no way to predict the weather. We had some miserably hot days in Germany and in Austria this past June.
If you're interested in castles and hiking, I think it would be a shame to skip the Upper Middle Rhine Valley when it's so close to Mainz. Like the Wachau Valley, the MRV is a supremely scenic UNESCO World Heritage site - and dotted with true medieval castles, vineyards, old-world towns and great hiking trails - like the Rhine Castle trail (Rheinburgenweg.) The MRV stretches north from the town of Bingen, about 20 train minutes north of Mainz:
https://mapio.net/images-p/6964886.jpg
https://upload.wikimedia.org/wikipedia/commons/e/e3/Maeuseturm_Burg_Ehrenfels_Bingen_Rhein.jpg
Old-world towns like Oberwesel, Braubach, and Bacharach dot the riverbanks.
Marksburg Castle and Rheinfels Castle are the most often-visited castles in this area and both are accessible to train users.
Rick Steves has Munich and the Füssen "castles" on a list of musts for a short visit. Munich aside, there is a lot of disagreement over the merits of visiting Neuschwanstein, the downside including crowds, the hefty admission price, the need for reservations, and the abbreviated tour time (30 minutes,) the hassle of getting there and back from Munich (nearly 5 hours by public transport on trains and buses) and the long walk once you're there. Rick calls N'stein a castle but Germans do not. According to at least one N'stein tour guide, many US visitors head there unquestioningly and do not believe him when he explains that it's not an old knights castle from the Middle Ages at all, but a late-1800's residential palace (with a deceptive and whimsical castle-facade exterior) that was built only a couple of decades before WW I. This DW article is worth a look before chiseling your itinerary in stone.
Should we rent a car or take trains?
Renting a car in Germany and dropping in Vienna will be expensive, since a car with German license plates will have to be transported back to Germany before it can be rented again. And you would not want to have one in Munich. Everywhere you mentioned has rail service. Sometimes, renting a car for a day to get somewhere out of the way is in order. Also, if you rent a car in Germany, you'll need to buy a Austrian vignette to drive on motorways in Austria, which you will need to do if you are driving to Vienna. Going the other way, an Austrian car will have vignette to start.
Thank you for the replies...all good information!