Does USB-C to HDMI take more processing power than direct USB-C to DisplayPort?
Technically speaking, your Macbook has two Thunderbolt 3 ports.  From Apple.com:


  Two Thunderbolt 3  (USB-C) ports  with support for:
  
  
  Charging
  DisplayPort
  Thunderbolt (up to 40 Gbps)
  USB 3.1 Gen 2 (up to 10 Gbps)
  




So, the adapters you have are actually Display Port to HDMI;  USB-C is just the physical port type.

So, the question is actually: "Which would work better?  Display Port to HDMI or Display Port to Display Port?"

Personally, I don't like converting signals from one to the next - I would go with a Display Port adapter and keep everything the same end-to-end.  The less you have to convert, the less overhead and the less compatibility issues.