I feel this is personal preference. I have done both but my preferred method is to, inconspicuously as possible, take several small back and forth stitches to lock the thread ends in place, bring my bobbin thread to the surface, take a good tug to ensure they are locked and then cut even with the quilt top. I do it as inconspicuously as possible to try and do starts and stops in the ditch, on the edge where it will be hidden by the binding, or in an area that already has a lot of thread build up such as a back track or place where the quilting has crossed over itself a few times. If this isn't possible then I knot and bury. I should also mention some threads are much more slippery than others so sometimes I have no choice but to knot and bury as the slippery poly threads just won't lock by tiny stitching.
People who do show quilts for big national shows knot and bury but I have entered a few biggies (MQX, Houston and Road to California) and did not knot and bury and still got high scores on my starts and stops (which means the judges could not easily tell where I ended or started a new line of quilting). If you get spiral eye needles it is fairly easy to knot and bury as you go with those, as long as you leave yourself long enough tails.
Many years ago, I took a class with Karen McTavish and she said she never knots and buries and has won a lot of ribbons on her quilts. She hides her starts and stops like I describe above.