I just discovered this last weekend how to fix the Kobo software problem with line spacing on ePubs (thanks to help from Mobileread forums). So I'm back to using the Kobo Glo in addition to my Kindle Voyage. The Glo (it's an old one) is noticeably slower on page turns than the Voyage, but I can live with that.
The software on the Kobo won't win any awards, but it has a lot more formatting features than the Voyage does.
Edit: The line spacing problem referred to is that side-loaded ePubs could not have the line spacing adjusted, and led to many, many books having double- and triple-spaced lines, or lines that nearly touched. Hard to read that way.