What do you believe in? As an incomplete basis for a good product - would you prefer a mess of code that is horrible to look at but works perfectly for what its supposed to do, or a beautiful set of well organized classes (or something else if OO doesn't float your boat) but have buggy functionality that still needs a lot of work?
If you were just handed a project to improve and work towards completion, which would you prefer? And what do you put the emphasis on when starting a new project?
I prefer both. However, if I was going to be handed a project I would go with buggy but beautiful everytime.
If we're talking about abstractions, I'd prefer to have just a small base set of working features. While it might be nice to have a pre-built, working library on top of this, the user can always create greater functionality from that working base.
Maybe they don't look nice, but again, a user can always just create a wrapper to make things look nice. I vote function.
Real artists ship - so something, that is both beautiful and gets the job done. But when in doubt, err on the "gets the job done" side, even if it isn't perfection.
Well written code will be easier to debug. If the code is too messy, even if it has "no bugs" (unlikely) it will not be maintainable.