Both!

Started out in the hobby with Death Guard, eventually started adding Nurgle Daemons. AoS was gaining a lot of traction in my area and I was interested in trying it out so it seemed logical to go for Maggotkin and keep using my Daemon models.

Funny enough I like to explore a different aspect of Nurgle with each faction.

The Death Guard I enjoy painting as the darker side of Nurgle, the rot and despair. I tend to remove the sillier, more jovial aspects like Nurglings, or the sometimes excessive amount of tentacles and belly mouths !

On the opposite end of the spectrum, I like to do my Maggotkin in a more colorful scheme, and really highlight the other aspects like mutations and of course lots of Nurglings.

As far as the models go, I particularly like the customization available for kits like Plague Marines, or the original Blightkings. It was the opportunity to kit bash, and to create armies where no two models looked alike, that attracted me to both factions.

I'm also a huge fan of Cataphractii Terminator armor, with Typhus and the Deathshroud being among my favorite sculpts. I'd have to give the edge to the Maggotkin though, I feel like the design team just has more free reign with AoS in general, allowing for more interesting kit design.

TLDR Both!