Both tests have their place. Blood tests are more accurate for total test while saliva is better for bioavailable test. For bodybuilders, we are more concerned about the bioavailable test as about 95% of our circulating test is bound by protein and is unavailable. Serum test would probably be more accurate for determining accurately dosed gear, but saliva is better to see how much you have available to use although this number tend to fluctuate more than blood tests.