I'm about halfway through my first listening of the soundtrack. Still a little too early to pick a favorite track. But the top candidates so far are Take You As You Are (original and slow versions), Rahzel's theme (original), Alzeid's theme (original), and Tabiji no Hate ni. Tabiji no Hate ni was one of the earliest pieces of music in the anime itself that caught my attention. It's used early in the series. Maybe as early as episode 1.
Edit: The vocal version of Take You As You Are (the insert song from ep 10) isn't included on the OST. Not even as an abbreviated TV version. I had thought it might be. Disappointed.
I'm glad I have a copy of the full version elsewhere because it's a lovely song.
I finished the album. The top contenders I listed above are still the top contenders for favorite OST track. I'm not sure I could narrow it down further. They each have their special attraction.