Six nights on a Balearic island.

I guess Mallorca is your best bet. There is good public transit to beaches and to smaller towns. I spent five days there without a rental car. I stayed in downtown, not at a beach resort.

It has been maybe 15 years or so, but we went to Mallorca, then took the bus to Port de Pollenca, on the east side of the island, on a bay. Lots of small hotels in town, good restaurants, good beach, several towns and sights nearby to keep you entertained.

At that time there were plenty of Brits and other Europeans, but reminded me of a small town resort, as opposed to the big package towns and non-stop party.

I admit that I have no idea what it is like now, but thought to pass it on.

I researched the Balearic Islands for my trip this year but ended up not having time for any of them. In the process I learned that ibiza is the party island, Menorca is the quietest of the three major ones, and Mallorca is the island with the most varied scenery and traditional tourist attractions. It also has more public transportation than Menorca. I would absolutely choose Mallorca without thinking twice.

I was just on Mallorca and Ibiza in March. Didn't go to any beach resorts, was just interested in the towns. Spent 4 days on Mallorca, based in Palma and did day trips (by bus) to two smaller towns. Then we took a ferry to Ibiza for two days, just stayed in Ibiza town. Ibiza has a reputation as a real party center during 'season' but was quiet in March. I would not want to go there in summer. I think Mallorca would be fine any time though.

Here's a link to my trip report and photos - https://andiamo.zenfolio.com/blog/2019/5/spring-in-spain---mallorca-ibiza-barcelona-tarragona-valencia