I can explain some of the differences and that may help with your decision-making.
Wengen is car-free and Grindelwald is not (although it does have a small pedestrian-only zone in the center). That makes Wengen a more pleasant place for strolling, to my mind. Grindelwald has lots of tour buses and other traffic.
Wengen is perched on a bench high above the Lauterbrunnen Valley, while Grindelwald lies in the bottom of the broad next valley over. Mountain views from both are lovely, although to see the full panorama of peaks from Grindelwald one needs to choose one of the hotels along the Panoramaweg, above the Main Street. Or hike or ride a lift up. Ut the Eiger North Face looms above the town and can be seen from almost anywhere that there is not a building blocking the view.
Grindelwald has more shops and restaurants. In Wengen, most of the restaurants are within the hotels, but non-guests are welcome to dine there. Guests can choose half-board (breakfast and dinner) at most of the hotels in either village, and if offered it is usually a great deal—some hotels pride themselves on the quality of their 4-course dinners, and justifiably so. Hotel Bären in Wengen is an example of such a hotel—-a comfortable, unfussy 3-star hotel with an excellent restaurant. Many of the hotels in both villages will be pricier 4-star hotels with spa facilities and other amenities.
Access: to reach either, you will take the train to Interlaken Öst. To reach Grindelwald, you board a train that will take you to the main Grindelwald station (make sure you get in the right car, as the train may split, with the other section going to Lauterbrunnen.) no further train changes required. To reach Wengen, you board the train at Interlaken Öst that is going to Lauterbrunnen (again, make sure you get in the correct section of the train). At Lauterbrunnen, you will change to a small cogwheel train that takes you up the mountainside to Wengen. Thus for Wengen, there is one additional train change, requiring carrying your luggage for the transfer.
However, when you arrive at the Wengen station, most of the hotels will offer a little electro-car or other transport means to meet you and take you and your bags, or maybe just your luggage, to the hotel. I don’t know if any Grindelwald hotels offer this service—-we have always walked through the village to our lodging there. But maybe others can advise you on this.
You may find a hotel you really like in one village or the other, and that can drive your decision.
