SAM mode launch won't give your enemy a launch warning, same for TWS. However, when in SAM mode, your radar will not adjust its elevation based on the target altitude, therefore, it is easier to lose lock when the target is dropping or increasing altitude (or the target gets too close it and goes below or above your radar elevation, which was set before you lock your target).
In contrast, in TWS mode while it won't give your enemy a launch warning, TWS will also adjust your radar elevation automatically to maintain a lock. Thus, TWS mode does not drop lock as easily as SAM mode does.
However, since TWS scan and lock takes longer than RWS, when you are in a hurry try to use RWS to lock your target and engage your target in SAM mode (not STT because they will receive a launch warning).
I learned all these from doing BVR in the Viper. Obviously, all the radar modes are WIP or not perfected at the moment. So in the future this might change.