Lodging in Grindelwald or Wengen?

Grindelwald has cars and tourist buses. Wengen is a car- free village. If it were me, I would spend the whole visit in one location,(Murren or Wengen) which is what I have done in the past. I have received better lodging rates when my stay has been 4-5 days in one place. Obviously not guaranteed, but that's my experience.
Enjoy your visit in this beautiful country! Safe travels!

We have stayed in both Grindelwald and Wengen (as well as Mürren) and enjoyed them all. Both Grindelwald and Wengen have their good points, and I will not advocate for one or the other. But I will suggest hotels, and maybe you can choose on that basis.

In Wengen, Hotel Bären, hands down. Take half-board there and you will get excellent food with gourmet-quality dinners, for a very reasonable price.

In Grindelwald, for something different, I might choose Alpinhotel Bort, halfway up the First Gondola at the mid-station. We had lunch there last September and I really liked the feel of the place. But I would probably only stay 2 nights there as you are pretty isolated. It is a great location for hiking, though.

https://www.huettenzauber.ch/en/hotels-accommodation/alpinhotel-bort

For a quieter place more in town, with fantastic views, I would like to stay at Hotel Bodmi:

https://das-bodmi.ch/en/das-bodmi-the-spirit-of-swiss-nature-2/

We have only dined there, but I was very impressed with the location, the friendliness of the hosts, and the quality of the facility and the food.

Do you mean you are going to spend 3 nights in Murren, then move to Wengen? It’s about 20 minutes away. Grindelwald is within an hour. I wouldn’t switch lodging. I prefer Wengen to Grindelwald because there are no cars.

Our stay at Hotel Edelweiss in Wengen was terrific! It's small, family owned, immaculately clean with great service from Daniel and his staff. We had a gorgeous view of the Jungfrau from our little balcony. They offer half-board, but you do not have to commit to that for the entire time when you book. We made a dinner reservation for our first night there, and then on subsequent nights we let them know if we would be there for dinner. Food was delicious and at a very reasonable price point. One evening, Daniel hosted a complimentary wine/cheese tasting and gave the guests a very interesting history of the area. Highly recommend.

I also wouldn't switch hotels. Pick Murren or Wengen and stay there. You can easily get to the other as many times as needed. You can even pop over to the other one for dinner and get back home afterwards. I found Grindelwald to be too hustle-bustle for my tastes. I found Wengen and Murren to be the jewels for spending my time after I was done exploring for the day.