I tend to apply Occam's Razor and choose abiogenesis as the simpler explanation. I see life as an inevitable/natural expression of complexity, and complexity as consistently increasing over time. The only question (in my mind) is whether or not there has been enough time for earth to achieve the needed complexity without outside input.

Since I don't know what the h*ll I'm talking about, I say "why not?".

On the other hand, intelligent design implies intelligent results. So it's unlikely to have created the weird mess we have.