I think I favour something more in the middle, I'm not going to care how pretty the art is if it's been so long since the last update that I don't remember what is going on anymore, on the other hand, and I'm not going to keep reading something if the art quality gets so sketchy that I can't tell what's going on anymore.
That doesn't mean that I'll refused to read comics for either issue though, I'll still read a series that takes forever to update or read a series that updates faster than I have time to read every time it does, and I'll continue reading it if I enjoy the stories and characters, but an in the middle balance it certainly something I enjoy running into. After all, who the hell am I to judge if I will read a series only based on the artists free time or work schedule?
Edit: Though I think I'm gonna have to side a little more with story progression if we're talking about how I like to release my own comics. I don't like feeling like I'm going no where or like I'm taking to long to get somewhere. I'm more interested in telling stories and moving forward than making sure everything is looking perfect. Not to mention, with everything being in digital, I can easily go back and fix or enhance it if I feel the need to.