Firm, fast.
Most of the (other) women I have shaken hands with have been limp and floppy. Learn how to do it, dammit. After a limp shake I usually want to wipe my hand on something. Be positive, be assertive.
Place I used to work was often visited by older posh blokes and they always greeted the women there with the double-cheek kiss. Yeah. I don't do that. First time a guy tried to do it to me, I stepped back and stuck out my hand.
Learn to do it. Being perceived as wimpy, no matter your gender, is just not clever.
If doing the handshake greeting for someone I did like - when they guy was landing 3 or 4 kisses on the other women - I simply added my left hand to the back of the shake so it would seem warm and friendly.
Do it right if you are going to do it.