The Relic Shield line is a better item to facilitate a singular person to carry your team, the Coin line is a better item to facilitate a team comp.
Relic Shield is the better item overall if you can make effective use of it's charges, since the gold income is comparable, and the shield essentially provides a health buffer for your carry. Coin is good when your team is on the same page, which can be tricky with randoms. Popping coin to retreat might be taken as popping coin to initiate, and vice versa.
The day will come when supports in High plat, Low Diamond will actually use the fucking relic shield...
#Believe.