Hand over slide, unless it's either of my M&Ps. Both of those will release the slide every time I seat a magazine anyway.
That - my M&P9 decides for me...
Works great up until it doesn't work at all, then you will stand there with gun at slide lock for about 3 seconds before you remember to do something.
Personally, I grip the top of the slide, forward of the ejection port, deep in the web of my thumb and index finger, this griping method is the quickest (for me) to reastablish a strong firing grip. And no, front cocking serrations are not required, I have strong hands, not girly keyboard commando hands