I have both Spark and Mavic Pro. Mavic Pro flies 10X better than Spark, but I have found it very difficult to dial in a camera setting that I like as much as the Spark. If you are making videos of wide open spaces, then a Mavic is a good choice. If you like to film architecture, or events, then Spark is a good choice.
If I fly 10 times, Spark is used 6 or 7 of those times. It's just easier to use, less invasive (people think it's cute), video looks good straight out of the camera (no color correction in post) and I don't concern myself with crashing the drone. The Spark can take a pounding, the Mavic Pro is far more delicate. If you crash the Mavic Pro, it's probable that the gimbal will be destroyed, and that's another $200 to $350.
Spark is for everyday people point and shoot
Mavic is for artists, and yet if that's your desire, go for the phantom 4 advanced, or pro, both of which have a better camera.
I look forward to a Spark 2/Pro with a 3 axis gimbal, 2.7K, gimbal follow mode in sport mode (as opposed to the horrific FPV), and free form mode in tapfly. Unfortunately, Spark 2/pro may never happen. I know there is Mavic Air, which has all of those features, but I think Spark is more robust, and will be more affordable; especially to replace.