I use 3 ton canadian tire type jacks with the racheting riser. I'll never use pins again, I hate those risky moments aligning the jack, and the rachet reduces that time. I also have a couple odd-ball screw collar jacks - I wouldn't put more than a drive line on them but that said they are the most useful tool I have ever had for lining up heavy parts within a millimeters accuracy.
I do use blocks and wood for bases - but guess it comes down to measuring risk. The closest I have come to toppling my jeep off the jacks was while wrestling the snot out of a siezed in front hub - temps that day got pretty hot and before I knew it the jeep started to lean. Luckily, I noticed the jacks sinking into the pavement before it fell. I think that's a point worth mentioning, If your working on pavement instead of concrete use a steel plate or suitable wood for blocking. I also almost always try to leave the opposite end wheels on which makes it almost impossible for it to tip off sideways.
We use wood blocking for both plows and tandems, and the plow units alone weigh more than a typical jeep, and the whole unit together is about 30 tonnes - I think the key point here is not to use crap wood - there are three woods that I use. I have a couple 3"x12"x12" douglas fir raw cut slabs for bases, these are cut off leftovers from the wood we use to deck our heavy equipment lowboy hauler deck (which has no trouble supporting a D6 ). I also use blocks constructed (again cut-off leftovers) from guardrail posts lag-bolted together. To ensure a perfectly flat surface I plate the top with recycled highway sign board - this stuff has so much epoxy in it, it wont delam or crack after 20 years of exposure and I have zero concern of it ever splitting as I harvest newer peices from signs taken down in accidents. I also pilot the screws holding the deck and have one for about every 4 " squared area - despite my confidence in the wood that I use, I still take the trouble to toss a secondary block under axles just in case. ( I saw a "faces of death" tape that had a guy die from an axle pinning and crushing his leg when I was in high school, I remember that tape everytime I jack up).
I guess the safest thing to do would be to use a couple steel 3/8 to 1/2 plates if a concrete floor isn't available, and with anything, redundancy, is important (extra safety blocks always)