Unless I need to unload the coils, I put quality jackstands--the kind with the solid iron, Y-shaped yokes--under the A-arms just outboard of the spring pan. In the rear I put quality jackstands under the leaf springs just behind the U-bolt brackets (don't want to mess up the threads of the U-bolts). Of course, you should be on level, flat and strong concrete only. FWIW, my BJ8 was suspended in this fashion and rode through a ~4-Richter earthquake without budging.
If I need to unload the coils I put a 2x4 under the chassis crosspiece by the radiator with jackstands on either side. I also use the 2x4 to jack up the front; on the rear I use the diff with a pan on the floor jack (that's a no-no for some cars like my Mustang, but I think the Healey axle housing can handle it).