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sweep is best when you have one uniform cross section. good example of this is the spring.
Loft is best when you have a body with multiple crosssections with different geometries. "example: flow channel with round inlet and a square outlet"
http://acad-atc.ic.polyu.edu.hk/inventor/02part.pdf
This will tell you all about what you can do.
What is easier? well that all depends on the sketch.