Yay! good mailing list font discussion. :) I'm glad you like my little font comparator! ^-^

So, here's my $.02:

I like the line-spacing of Cantarell better - it makes reading from line to line easier, and I like the glyph shapes for the most part, as well. But there do seem to be some kerning issues as Paul pointed out. It doesn't look quite as polished as Droid. And for some reason (probably just me being OCD) the lowercase 'a' is bugging the crap out of me. Every time I read something in Cantarell, that 'a' catches my eye. Aside from my own weird glyph obsession, it also doesn't actually cover (as far as I can see) the cyrillic or greek scripts. I believe it's just using the default serif font to display those scripts. So, if that's an issue, we'll need to either pick another font to cover them, or get those scripts added to the font (volunteers?).

I find Droid easier to read on a line, and at smaller sizes. Droid also does have cyrillic and greek, and according to wikipedia, it's supposed to have CJK support? ¯\(°_°)/¯ And to me, it's cleaner looking... but that's just an aesthetic preference.

Grr, I'm really conflicted here. I think aesthetically, I like Droid better overall, but Cantarell is open and source-available, so even though it has some issues, we can fix them...