Should I use S110, S120, S130, S210 or S310 ?

[Thomas]

I have bought the nRF51 dev kit. I can download all these soft devices. But what do they really correspond to ?

I think of them as library/apis for doing BLE development but why are there so many, which one should I use ?

Thanks

[mohBOSS]

Since you have 2 nRF51 DK, you can use one as a broadcaster(with S110), and the other as an observer(using S120).

Best.