Interlaken area and type of passes

Hello Vibha! That's a bit hard to say, as the price difference between both options can be quite small. The only way to find out is to make calculations based on (estimated) list of travel plans. You could consider that the Swiss Half Fare Card is valid throughout the country. That's convenient if you expect to make trips outside of the Bernese Oberland (Lucerne is an example), or if you want to have this freedom if weather in the Bernese Oberland happens to be bad. On the other hand, the Regional-Pass offers a number of days with free traveling. If you plan to use cable cars and mountain railways quite intensively on some days, the Regional-Pass allows you to do so (with some limitations of course).

Note that children travel along for free on a Swiss Half Fare Card (with a free STS Family Card), but not on a Regional-Pass. You have to buy them a Junior Travelcard (CHF 30,00 per child) in that case.

I know this isn't a decisive answer, but I do hope it helps you out.