We've done many TS trips to Europe, each 3-4 weeks, and of those mentioned here, some favorites and comments:
Portugal! I had overlooked for so long, finally booked when we'd been almost everywhere else on the list. Can't wait to return, and if we ever have to leave the US, it'd be #1 on my refugee destination. It's a small country so driving wasn't bad, very diverse and stunning landscapes. The Cascais TS is an easy train ride into Lisbon, other not-to-miss areas are Algarve, Douro Valley + Porto.
Switzerland: been 2x now, 4 total TS trades, and if we lived in Portugal I'd go every summer. No need for driving because public transportation is so reliable. Bernese Oberland /Lauterbrunnen Valley + towns still my favorite but last time we also traded into the TS in Leukerbad, Les Naturelles, which was gorgeous - it required more travel time to get everywhere we wanted to see.
Austria: 3 TS trades into Bad Gastein, Grundlsee, and Vienna, loved them all, especially the first 2 Mondi resorts. Car recommended for things like driving the Grossglockner High Alpine Road.
Italy: loved Italian Alps for summer hiking (often overlooked), have been there 2x, also we traded 2x into TS's in Venice, and once in Tuscany where Florence wasn't too far by train.
Wales Pembrokeshire coast! Another often-overlooked destination. Have traded into TS's in St. David's and Haven Court. Both were excellent, St. David's better to avoid driving where yes it can be challenging - however you probably want a car to depart at dark-0:30 to reach the ferry for Skomer Island -- which matches Switzerland for my #1 destinations ever witnessed, we have been 2x and I wish we could return every June.
Many others to mention -- loved Brittany in France but we didn't do a TS trade there, loved the Perigord region of France, yes TS trade and yes car required.