I am not sure you are framing the photos so we can tell if the wood is placed well. The most prominent part of the wood needs to be somewhere around 1/3-2/5 from one end or the other to be most comfortable for our eye. We need to see the whole length of the tank.
I like both scapes and I liked the first one too, just place them a bit off center and any would make up a nice picture for you. For a 20 long I might be leaning toward the one on the left as it implies movement with the long diagonal top edge which complements the long low tank shape. I would place the heaviest part of the largest bit of wood at the sweet spot first and see how that looks.
There are a lot of good threads here on developing your eye for satisfying scapes, here is one.