Rockwool, some sware by it, im a new grower myself... but ive tried it a few times I hate it, horrible luck, good soil and i was totally set. Depends on where, what lights, what strands... I guess it all makes a difference but im a straight soil guy I think That one on the left looks really good, do you not have a fan on them? There gonna get weak without a decent fan! I have my fan on pretty much 24/7 there little 2" right now, really leafy... very healthy SO FAR... strong... eh