Best base for the Salzkammergut ?

Why not Gmunden?

How about St. Gilgen?

And what about telling me which one is better between Bad Aussee and Bad Ischl ?

I prefer Bad Ischl

As you want to explore the Salzkammergut you should not choose a base which is located in the most distant corner of the area.
I still vote for Gmunden.

Thanks for those answer.

I don’t see how Gmunden is much better than Bad Ischl location wise. It’s farther from Hallstat and most of the lakes.

The better base is Bad Ischl. That town has good public transportation connections to the Wolfgangsee and Hallstatt as well as to Salzburg. Bad Ischl also has a bit of interesting history.

Bad Aussee is closer to a couple of less popular lakes that you would probably not otherwise visit.

Both are charming Austrian towns, but Bad Ischl makes a better base for the things you would want to see.

How are you traveling? I've only driven thru Bad Ischl and never been to Bad Ausee. Just looking at the map Bad Ausee looks to be an outlier. But, if that region is your focus than choose it. I've never been to the Altaussee and its on my list to visit. 3 nights two days focus and enjoy your time.