If you care about OOF character there are certain lenses known for having "good" or "smooth" attributes. In my experience these are:
Nikon 85/1.4, 105/1.8, 105/2.5
Leica Summicron 50/2 Dual Range, Summilux 50/1.4 Asph
Any Sonnar copy, I -love- the way my Jupiter 8 50/2 renders out of focus, really soft.
Hasselblad Sonnar 150/4, Sonnar 250/5.6
Pentax 67 105/2.4, 165/2.8
Schneider Xenar 127/4.7 and Symmar 210/5.6
This is subjective, but these are the lenses that I have used that exhibit really smooth OOF areas. That said, I have -never- chosen a lens because of the out of focus rendering, preferring to make my selection based on size, and speed (I like fast lenses, and not running out of usable f/stops).
This is the Symmar, excuse the fact that I dropped the polaroid in the grass after I shot it.
Jupiter 8 50/2