Tracing (convertion bitmap to vector)

Is there a better app to convert a graphic into a bitmap? Even though a PDF is generally considered a vector, it would be nice to have a way to take a drawing and create a generic vector drawing of it. Nothing fancy.
Corel Draw used to have this in Corel Trace and I saw some apps on the App Store for converting but don’t know if one is better than any other. Any suggestions?