How to choose? My only comment is that the series title is so much larger than the book title. I would reverse that so people don't think they're reading the same book but with a newly released cover. "A Voice at Culloden" is more appealing to me than "When Gods Clash". When quickly glancing across your post, I thought they were all the same book.
Typeface comments by others seem legit. Is 'clash' the word you want to use?