Corrected version for the bold one and a different /a/.

(Does /a/ look relatively small below?)

The way you ideally do this is, you don't tell us what it's supposed to be, you just ask to read it. :-)

That said, all of them seem entirely legible to me (in context).

But: the gaps in "k", "n" and "s" should be bigger (at least at normal sizes).

hhp

The single-story seems to gel with the rest of the logo better, as it is more open and geometric, but my vote is for the double-story since it will not be confused with an o at smaller sizes. The double-story a is a little heavier visually than the rest of the lettering, but only slightly. You asked if it looks small, but I don't see that at all, so I think you're ok there. For what it's worth, the thinner weight of the two looks much better to me, more natural.

For fun, here's the a both ways:
http://www.myfonts.com/fonts/gtandcanary/morebi-rounded/
http://www.myfonts.com/fonts/canadatype/vox/

@hrant

Good point on how I'm supposed to ask it :D

About the gaps, you're right. I had a legibility concern there too. I fear the /k/ for instance could look like "I <" when the gap gets bigger.

@_Brian

Thanks, exactly what I think about the /a/. I thought it could read as /o/.

About the size of double-story /a/, you described the problem better, that's what I'm talking about. Single-story blends much better with the rest of the letters.

Those fonts you linked are great by the way. I'll study them.