This post is a follow up to the previous "Transpiration from Graz to Hallstatt " question i had. Having contemplated renting a car or taking public transport (train+bus) and opting for the later, i hope my feedback will be helpful to those who are considering the same:
If i could do it again, i would rent a car. No question about that.
The trip was costly, required 2 transfers (train-bus-bus), and lasted 3+ hours. The transport routinely ran late which caused for concern (turns out they do wait for you at transfers though).
If you are staying overnight in Hallstatt, book the room that includes parking (although overall parking in proper lot didn't seem like that much of a problem for others either). Having a car will also let you stop by and check out interesting towns along the way at your leisure.