I only own a Spark and I was also torn between buying Spark or Mavic. Got the Spark but kinda regret that choice for the following reasons (random order)
1. "Only" HD on Spark vs 4k on Mavic. I thought I could live with HD and I can but 4k leaves more versatility in editing and cropping your videos.
2. Color profiles not available on Spark. Eventhough image quality on Spark is good by all means, not having color profiles makes it more difficult to create the look and atmosphere you have in mind.
3. 2 vs 3 axis mechanical image stabilisation. Spark has a 3rd axis stabilisation but an electronic one and you do see some artifacts of that sometimes.
4. Reliability of the radio link. I don't need the range of the Mavic but the fact it can go further means the link has more headroom, also on short range. I did experience link stability issues with Spark at ranges much shorter than those advertised by DJI.
5. Use of OTG connection with Mavic remote. Imo it is common sense this is a much robuster connection compared to wireless. Again did experience issues with this wireless link of Spark remote.
6. Flight time. Found myself having to land much earlier than I liked to swap
batteries on Spark.
In the end, most of these points indicate I have outgrown the capabilities of the Spark much sooner than I thought I would. It is still a good drone at a very accessible price for what you get and I still enjoy flying it but it has limitations that Mavic doesn't have.
Up to you to consider if the limitations I'm experiencing after using Spark for a while, are of significance to you