I prefer IntelliJ's git interface.
Magit can do everything IJ can, but in IJ, I can find how to do things more easily and it just feels easier to do things, probably because it's much more GUI than text compared to Magit. For example, difficult merges are extremely easy in IntelliJ, I can edit code in the diff view itself while I resolve conflicts... in Magit it requires getting used to the different diff views, something I am still trying to figure out, but it seems trickier to do "in-place" changes in the code.
That said: I probably only prefer IJ because I've been using it much longer than I have used Magit... and the difference for me is very small, so I suspect the more I use Magit, the more the gap will close and I may eventually like it even more than IJ.