all are amazing tanks. not just saying that, i mean it.
However, I do think it's a toss-up between #1 and #6 because it seems to me that they'd require the most effort to maintain (Is that BBA in #1??? Great job). All the others are pretty simplistic (which is understandable when dealing with bigger, aggressive fish). #5 is really awesome and pretty, but to me personally, the lack of plants and the consequent lack of color variation and vibrancy is what places it behind tanks #1 and #6.
My Opinion/reaction
#1
The drift wood on the ends look great and helps "wrap" the presentation of the tank, but if they reached just a bit further and also had a branch or two reaching down it would give it a more natural look.
#2
The hardscape and the plant density gives the tank a good natural look, but the hornwort... i don't really like it. Good tank tho.