We really like to rent a house or apartment, for a few weeks, in a town/city/village that's convenient for day trips by train and car. Any suggestions regarding Alsace?
check on gites-de-france.com
If you include Lorraine in the search for Alsace you may get all sorts of results west of Alsace. West of the Vosges, including Nancy. If you only want Alsace I suggest limiting yourself to there.
Plenty of places meeting your needs in the vicinity of Colmar and Strasbourg; Mulhouse has never appealed to me unless you want a load of time in the car museum; northern and northwestern suburbs of Basel, Switzerland are also in Alsace.
For your day trips do you have an idea of where you'd like to daytrip to?