Don't use either.
The only answer is tons of organic material...manure, old compost, etc, added and dug into the soil at this time of year, then left over winter until spring.
Then repeat for several years.
And the word tons is the main word.

if it helps we moved into our house last year. we have heavy soil between 5 to 10 inches deep, then clay. i have tried digging down into the clay, after still finding clay 3ft deep i asked the same type of question, and the answers i got were basically the same. compost, compost and more compost. to be truthful it has been hard work but the results are starting to show. the ground does not seem to be sodden like it was. the other advice i was given was to try raised beds, but i prefer open ground. so good luck and i hope it all works out for you. muddy