parts.io is a new parametric search engine for parts. Supposedly it's claim to fame is that it finds parts from all distributors (like octopart) and presents a more complete picture on the lifecycle status of a part (super important). It seems to have promise, but I don't think it's better than digikey yet.
I liked the way parts.io presented information. After I make a selection in digikey, it can be hard to undo it or find out what selection I even made. The UI for parts.io is definitely better.
My main problem with parts.io is that it doesn't seem to know very much about electronics. If I'm making an RF filter, I can't use general purpose capacitors for it. Digikey makes it easy to select only RF rated capacitors. Parts.io doesn't even seem to know the difference exists.
Parts.io also has a units problem. Large or small part values are displayed in scientific notation with no units. The standard prefixes (k for kilo, M for mega, etc.) sometimes aren't recognized by their search engine. It also turns out capacitances are displayed in uF only, which is somewhat non-standard.
parts.io seems to have the right idea, but I'll wait until they're out of alpha to actually start using them.