I think Resilent: Con is an A-tier pick.
I've done simulations comparing Warcaster and Resilient. On average, War Caster is +3.2 to your concentration saves. As soon as you hit level 5, your proficiency bonus is +3, so Resilient Con is just -0.2 below that. However, perhaps that +1 to CON bumps you up to an even number, meaning it's now +0.8 better than War Caster. And it applies to things other than Concentration checks.
At 9th level, your proficiency bonus is +4, and Resilient Con is undoubtedly better unless you have a particular need for the shocking grasp reaction.
So in summary, early game War Caster is slightly better. By level 5 it's about a wash but I think Reslient is better overall and especially if it lets you hit an even number for CON. By level 9 Reslient is undoubtedly better.
