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I would consider the "best" way to balance egress traffic would be using PfR, this assuming your equipment supports it.
From what you describe, 2nd best (for a single edge device) would be to direct all traffic to it (single default route to it) and allow it to use BGP ECMP. The latter requires BGP routing be configured to support two paths, maximum-paths 2, and usage of the hidden command bgp bestpath as-path multipath-relax.