Good Question: To me it seems like when I watch videos it is a toss up for which is more common/natural between people doing leading and trailing tail grabs. I struggled with this for a while and kept trying both, in a leading (Spin L - L to L) the tail is right there near the hand that leads the spin so it's easier/quicker to grab, but I've found that in bigger jumps with more time it tweaks better for me to grab my trailing tail and then "pull it around" with me as my trailing hand completes the spin. Keep trying them both watch it on video and decide yourself.