Never, ever trust your parking brake. You sound experienced enough to know this but others might not. As proof stop on a steep hill, put the parking brake on with the car in neutral and let your foot off the brake. Most cars will roll. If not, have someone push on the uphill side of the car-it almost certainly will roll then. ALWAYS chock at least two wheels, on both sides of the wheel.
The problem with ramps is they can fail, or people can improperly use them. I've driven off my current set a few times (slippery ramp, standard transmission front wheel drive means its hard for a klutz to get up the ramps right in wet weather (I work outside)). The side support beams can become twisted and the ramp is much less safe then. Or you may not have the car all the way up properly so the wheels are firmly set in the wells.
Jacks are undoubtedly safer. Ramps, in good condition and properly used, are safe enough for such things as oil changes. If I'm going under the car a long way or time, it's always jackstands for me. An oil change the ramps and chocks are good enough.
People above mentioned the problem of ramps slipping on your garage floor when you drive up them. The bolts in the floor will work fine, but a far simpler solution is two pieces of scrap 2 x 4, one in front of each ramp to the garage wall to brace the ramp. Simple to use, no fuss and no permanent damage to the floor.