For solo shows, I like to play someplace where I feel like there are people in the audience who are paying attention to me. Ideally this means that my friends are there, but if not, then other musicians can also be a good audience. (I would rather play for a small audience with a few of my friends in it than a big crowd that I don't know and which doesn't seem to be paying much attention.)
For Killdevils shows, Chris and I can operate as each other's audience to an extent, so it isn't as important to me that the audience be paying a lot of attention. Also, I tend to think that the music is more of the focus for these sorts of shows, whereas my solo material the focus tends to be more on the lyrics and singing, so I don't think it takes as much concentration to get some enjoyment out of the Killdevils set, whereas for me playing solo I think if you're not listening to the lyrice I don't know how much I stand out. So playing in a bar like Nickanees, which sometimes is full of loud people and other times is virtually empty, is OK as a Killdevils venue, but I don't think I would want to play there regularly as a solo act.
In either case, though, it is difficult to find gigs, so I (or we) don't usually get to pick and choose.
(Getting paid is also a plus.)