Put the UHF on top. Combine them with a UVSJ (UHF/VHF signal Joiner, cost less that $10 and looks like a splitter, but more complex).
Your best friend is elevation, like your neighbor, he has 20 ft of elevation advantage on you, so your antenna(s) may have to be 20 ft higher to get into the same signal soup where his antenna sits.
We had an old analog station (channel 8) for our NBC that was 82 miles away, so everybody in town had a 40 ft telescoping mast mounted in the center of their roof, guy wired to each corner of the house, and everybody got a good clear signal (back in B&W days).
Another thing is, get a preamp and install it up near the antenna with the power injector in the house (no splitters between the injector and the pre-amp), that should help too.
Winegard has just come out with a couple of new low noise (~1dB on UHF) pre-amps, the LNA-200 might be what you need, but it's $70 - I have no experience with them - just a suggestion.
Hey, fringe reception ain't cheap.
You might even start filling the cookie jar to get you a 60 ft tower to mount your antennas on (put it on th e up-hill side of the house).