I made the switch from rotary to rack and although I've seen some very smooth, easy to steer racks (pretty much every one in fact), I must've gotten a bad one. Mine's really notchy and you can feel each tooth as you turn it. I've played with shimming it and such, in hopes that it was just a clearance issue between the rack and gear, but nothing seems to help.
The change over went real well (had to redrill some holes) and there was plenty of room to install the rack. I'm just not real happy with it. In retrospect, I should've taken the thing back to where I purchased it from and had them order me another, but I didn't. If it's not necessary to switch, I'd just leave the rotary in it, and buy a new cable for it. You can disassemble the box and grease it up, install the new cable and you'd be good to go. I had changed the cable on mine once before I made the switch, and it was smooth as butter when done. Not a difficult job to install the new cable.
2 cents worth from someone who's been there and done that.
P.S. In my opinion, neither is safer than the other provided they're in good condition (gears not overly worn etc.)