Yeah, picking between those two can be a close call. For this tier, however, I feel like having LS is more useful seeing as it's more effective for Ragnaros. You can in fact calculate which choice is better for you at this site: http://theincbear.com/living-seed-replacement
Results for me were the following, putting LS clearly on top:
Blessing of the Grove: 0.18947395801971106
Living Seed: 0.3
Natures Bounty: 0.9405405405405406