Just to be clear on one thing, the official power levels of the show are non canon. Allow me to explain, at the beginning of Dragon Ball Goku at a power level of 10 could lift 10 times his own weight, then at the Namek saga he had over come a hundred times normal gravity, however once he got into the Majin Buu arcs he had to turn super saiyan in order to lift 10 to 40 tons of weight, total bull crap.
And speaking of the Buu Saga, according to it Goku was weaker in his fight against Janemba then he was against Cooler's fifth form. The official power level says that super Gogeta was 2,500,000,000. Divide that by 400, the power boost of a super saiyan 3 and the total is a little over 6,000,000, that at super saiyan, which is times 50, is over 300,000,000. Coolers official power level in form 5 was at 470,000,000. That mean that fighting Cooler Goku's power was 10 to 20 million, yet it was 5 million or lower against Janemba, total bull crap.
Don't get me wrong I love Dragon ball Z, and now that I did my rant allow me to show you, through much calculations, with pieced together information based on preset standards, since very few times anything is kept straight in either Dragon ball Z, or DC characters, who would be the more powerful.
First off strength, that depends on which version of DC your talking about because it changes and fluctuates depending on the writer, with superman going from lifting or pressing 100,000 tons to 6 sextillion to 200 sextillion, and yes it is spelled sextillion I looked it up it, is a 1 with 21 zeros after it. At there weakest DC is nothing to DBZ, at their strongest it is the other way around, it depends upon the writer, but because of that the Justice league are powerless unless someone says how strong they are which is a huge weakness for them.
For Dbz it is more defined, for every 1 unit of energy the main characters can lift their own weight again so at a power level of 10 Goku could lift 10 times his weight.
When he met Raditz, his weight was 137 pounds, and his max power level was 410, 137 times 410 equals 56170, and there are 2000 pounds in a short ton so 56170 divided by 2000 equals 28.085 tons. That is pretty strong so far. In the orginal manga when Goku fought Nappa his power level was over 8000, not 9000, so 8000 times 137 pounds equals 1096000, divided by 2000 equals 548 tons, That makes him incredibly strong. When he used the Kaio-ken (pronounced Kai-o not Kay-o for those who don't know) on Captain Ginyu, his power level was 180,000, that was 22.5 times more powerful then when he fought Nappa, so 548 multiplied by 22.5 equals 12330 tons lifting capacity. When he finally met Frieza, Goku's power level was 3,000,000, a total 375 times stronger then when he fought Nappa, so 548 multiplied by 375 equals 205500 tons, using the kaio-ken times 20 would make it 4,110,000 tons and going super saiyan would make it 10,275,000 tons in total. Against Cooler I would assume his super saiyan power at 600,000,000 so his over all strength at that point would be 41,100,000 tons in total, So the Z warriors might not be as strong as the absolutely strong superman, all the other justice league heroes are screwed.
Second off, speed. The Fastest would Be the Dragon ball Z characters. Older Speedsters like orginal old Flash can run at 770 mph, while those in their prime can move as the speed of light, and superman at his fastest was seen running along side the Flash at mach 9350, that is 9350 times the speed of sound.
When Goku went on snake way the first time it took him a total 6 months. However since snake way is constantly Zigzagging the entire way along with the occasional loop it is fast to fly over it so flying could cut it down from 75% to 50% time.
Assuming it is the 50%, a jet flying at the speed of sound, or mach 1, which is 761 mph would get there in 657 hours or 27 days. Goku did it in 28 hours on his second run, meaning he was going at mach 23, 17503 mph! When he faced captain Ginyu, he was at mach 517.5, or rather 393,817.5 mph. Against Frieza he was traveling at mach 8625, and at super saiyan it was mach 431,250, or rather 328,181,250 mph. The speed of light is 186,000 miles per second, there are 60 seconds in a minute, and 60 minutes in a hour, so 186,000 times 60 equals 11,160,000 times 60 equals 669,600,000 miles per hour. That means Goku was traveling at roughly half the speed of light.
Cooler at his fifth form had a power level of 470,000,000, meaning matching it would give a speed of 1,028,301,250 mph, almost twice the speed of light. Goku when he beat him had to have a power level of 600,000,000, creating a speed of 1,312,725,000 mph! So any body stronger than Cooler was as fast or faster than superman and the Flash.
Third and maybe most important, pure destructive power/capability. Do I even have to say it? It's none other than Dragon Ball Z. Why you may ask? Two words. Ki blasts. Since the beginning they have been the source of great destruction. Since the very first Kamehameha technique used by it's inventor master Roshi, Ki attacks have been used to win the majority of battles. Roshi's power was only between 100-200, at that power Goku could not lift a whole lot, yet the Kamehameha was used and it completely destroyed an entire mountain, and in one of the Dragon Ball movies, the path to power, it obliterated the entire naval forces of the Red Ribbon Army. It also has been revealed that some techniques channel their energy to certain parts of their body to concentrate and enhance their power drastically.
Once the power level was at 200-300 a area blast could reduce a city to ashes and a Kamehameha technique was capable of destroying the moon. And every 18,000 units could blow up a planet. In DC the Characters were stronger but never had that kind of power, and often were terrified by it, and usually if they did have a energy blast destroy a planet, it was almost always a doomsday weapon and does not count, also as a power level increases, the durability of the owner increases, so they get more destructive while being harder to destroy in the process.
So in conclusion While DC characters are physically stronger, in terms of speed and blasting based powers they are completely out classed and are not nearly as powerful as the characters from Dragon ball Z.