I'd recommend getting both Pixelmator and Affinity Photo/Designer. There is overlap but not 100% and they have different approaches and strength and weaknesses. Affinity's interaction model is closer to Adobe if you are coming from that suite. Pixelmator has some unusual features like this. I use both when needed.This is really tempting! I've been working with gifs a lot more recently for sharing dev work, and while photoshop does a decent job, it's a little clunky. Giphy and other online gif creation services lack some finer control. Pixelmator might be worth a pickup for that feature alone.
I've also been eyeing the Affinity apps too. Been debating the jump from Adobe for a while now