I would be happy with either, but honestly.. I am not sure which I would prefer.   
  
"Project of Eternity" 
- Showing off my "I was there from the beginning" attitude. 
- Representing being a kickstarter supporter.   
- Plus sometimes the codename is cooler (Sega Katana, Windows Longhorn, Nintendo Revolution) 
  
"Pillars of Eternity" 
- Much more Relevant   
- New comers to the game will know what the T-Shirt means, not just early backers.   
- Sometimes the real name is better than the codename (Nintendo Dolphin, Blue Harvest, The Burly Man)   
  
Disclaimer: I like both names just fine.   
  
PS: This is my first day on the forums.. If this has already been discussed, then please ignore.