By far the best (and most expensive) is the SDI E-Clik Shocks. We’ve got them on our XD 1500 with JRI Mid Travel suspension. They’re electronically controlled, and you can switch between ride modes on-the-fly. They have presets like Highway, Trail, and Desert but you can set custom settings to fine tune the ride.
Then SDI also has their Trail master Shocks. They’re a standard shock with manual adjustments, but still a massive improvement over OEM.
We’ve had Z Bros on our previous Ranger XP 1000 Crew with HCR, and they were great as well.
And finally, Shock Therapy has shock upgrades for the XD 1500. I don’t have any experience with these but S. T. typically does excellent work and I don’t think I’d hesitate to try them.
Any upgrade is going to be a huge improvement over OEM.