Great discussion. I generally agree with the above points, but I'll add my two cents because I tend to differ from the majority of posters on these forums. First, I always rent a car rather than use the trains. Although the Swiss trains are great, I really like the flexibility of having a car for taking day trips and getting around the Berner Oberland and surrounding areas. From Lauterbrunnen, we've taken side trips to Lucerne, Bern, Meiringen, Interlaken, Murten, Lausanne, Zermatt, Kandersteg and Thun.
Second, I don't stay in hotels. I use VRBO to find apartments with a kitchen, sitting room, and a balcony with a view of the mountains. We've been to the Berner Oberland three times (a total of 32 nights) and stayed in Lauterbrunnen and Grindelwald. Third, hiking in the mountains is my major priority. Proximity to the lifts and mountain trails is important to me. (See my profile for a trip report and discussion of hikes in the Berner Oberland.)
Regarding costs, if it's just my wife and myself, a car is a little more expensive than two train tickets. Sometimes we travel with another couple. In that case, a car is definitely less expensive than using the trains. Also, I've found that a VRBO apartment is about the same cost of a hotel room for two persons. A two-bedroom apartment is definitely cheaper for four persons (with a lot more room). I've stayed in a very nice two-bedroom apartment for $150-160 per night in both Lauterbrunnen and Grindelwald.
Regarding Lauterbrunnen versus Wengen, I think Lauterbrunnen is interesting and a fine location, but Wengen has gorgeous mountain views. I've never stayed in Wengen but I've walked through the village several times and taken hikes that started there. But if I wanted to stay in a car-free village high in the mountains, I think I'd choose Murren for the reasons discussed above by other posters. Also, although both villages are close to many trails, I personally like the hiking trails around Murren better. It's also relatively easy to get to all of the excellent hiking trails from anywhere around the Berner Oberland.
In addition, I prefer Grindelwald to Lauterbrunnen (even though both are very good bases IMO) mainly because of the greater number and choice of restaurants. I know many posters will not agree, but I don't mind the somewhat greater size or number of tourists in Grindelwald. I spend most days on the hiking trails, however, and with a car, I can easily get to Lauterbrunnen, Stechelberg, Murren, Wengen, Gimmelwald and other nearby locations quickly -- or go into Interlaken for lunch or dinner, or sightseeing in Bern, Thun or Meiringen.