Hello. I do not know that one is any safer mechanically than the other but for most of us, the frame-mounted thumb safety is usually easier to operate quickly. It is in a more natural location to be pushed down (for fire) and up (for safe) compared to the slide-mounted safety which almost always operates in the reverse (down for safe). (Makarov pistols have the slide-mounted safety and are an exception to the "rule" in that their slide-mounted safeties operate in the same direction as the frame-mounted ones.) Because the slide safety is by necessity higher than the frame-mounted ones, many find them less comfortable to use at speed.
Most slide-mounted safeties also serve as a hammer drop such as the S&W, Beretta, Bersa and Ruger, to name a few but again, there are exceptions. (The Star Model 28 has a slide-mounted safety and does not drop the hammer.) Frame-mounted thumb safeties usually don't drop the hammer when engaged but again this is not a hard and fast rule for some do, such as the Beretta Model 84.
Best.
Best.
Most slide-mounted safeties also serve as a hammer drop such as the S&W, Beretta, Bersa and Ruger, to name a few but again, there are exceptions. (The Star Model 28 has a slide-mounted safety and does not drop the hammer.) Frame-mounted thumb safeties usually don't drop the hammer when engaged but again this is not a hard and fast rule for some do, such as the Beretta Model 84.
Best.
Best.