Single Region vs. Global

ELB provides single-region failover and load balancing while Route 53(R53) operates at DNS level so that can failover across regions.

Instant Failover

ELB routes traffic off an unhealthy target (like an EC2) immediately when it is detected while R53 operates at DNS level, so when a client endpoint have cached DNS results in their DNS resolvers, it will not be effectively redirected until it passes TTL.

AWS vs Non-AWS

ELB performs failover within the AWS target groups where only AWS resources can be registered. R53 operates at DNS level and is resource type agnostic.