I like the third one and the last one... However i think it would look better in the last one if you placed it in the back of the tank and kind of had the branches poking through the plants. However looking at your tank it looks like that is not an option unless you want to uproot all of those plants in the background
i was just playing around with the pieces and have decided on the last pic, i moved the wood back some and cut some off to do so. it looks the best so far so i think ill stay with it for awhile.
i rescaped alittle and have the right side of tank looking ok. the left side i will rescape after i get some more plants.