I don't think it's about level as far as status or spiritual heirarchy...rather level of intricacy of preparation....
It's like a comparison in music between say, Beethoven and Folk music. One is not higher that the other, but one took much more time in the composing.
Or the difference between DaVinci and Grandma Moses in Art.
"High" magic involves years of study and each ritual/spellworking takes literally months of study and preparation. In "Low" magic, we might grab a few herbs and colored candles at the Magick shoppe and put something together in an afternoon.
And i am not qualified to make a judgement as to which is more effective. I think that's about the individual/s doing the spellwork.