My suggestion would be to get both on Audio Book. They do Star Wars music and sound effects and even "zombie" sound effects. I didn't read the books because I got these, but I'd say if you like OT type stuff, Death Troopers ties in more to that. If you like Old Republic type stuff, Red Harvest has the Sith behind it which made for probably a better or more interesting story.
I don't think you can go wrong. I'll predict whichever you get, you'll want the other once you're done. (I did Death Troopers first just FYI)
I hated both. Disliked them even more than "Jedi Trial" which had been my least favorite Star Wars book to that point. Zombies and Star Wars just don't mix. No Star Wars feeling at all, and doesn't work as horror book either. Waste of money.
I preferred Red Harvest over Death Troopers but really don't like the zombie/horror element being brought into Star Wars. I'm repelled by dwelling on gore and rotting and the means of death and dying in horror movies. I prefer more intellectual fear than the blatant showing of the thing to fear. But I think why I'd say Red Harvest is that I thought it had elements that were different from what I am used to.
It's a big galaxy so if forced to, I could tolerate the idea of a disease that would seemingly kill but keep you animated. I just wish they'd have toned down the horror aspects of gore. Just have the problem be how to halt the disease, how to fight those who won't stop/die, how to fight those who were your friends. More psychological terror. All the disease/zombie descriptions were quite disgusting for my tastes.
But for whatever reason the general populace has been stuck on zombie fascination for many years now, so I guess I shouldn't have been shocked that it would creep into Star Wars, but I was surprised and disappointed.