It comes down to if you have a shield Cleric in your party.
The Shield of Life is one of the best shields for Clerics, useful through the entire mid-to-late game.
It's not a deal breaker, as there are other shields that have equal defense, just with different elemental protections. The
Red Leather Shield, will be useful all game due to late game fire damage.
In the early, to mid-game, toxic/poison resistance is limited. But the late mid-game you should have plenty so the ring will help till than.
So final best advice:
If you are playing with two shield users, including a Cleric, grab that shield, but the ring is totally fine, too.
If you are playing with a single Shield user that is a Cleric, players choice, with a lot of leaning towards grabbing that shield.
If you are playing without shield users, or without a Cleric, get that ring.