Treacherous Covenant: A very potent flat strength increase while you are above 50% health. If you can guarantee the uptime of this trait it is a very solid Single Target and AoE option.
Frostwhelp’s Indignation: Having multiple of this trait can make it strong, but compared to the other traits in my option it just fall short.
Frozen Tempest: Extremely strong in M+ or heavy AoE fights.
Echoing Howl: This combos really well with frozen tempest for heavy AoE fights or M+.
Recommended Azerite Traits
Single target Azerite Traits
For Frost DK, as most traits are pretty close for single target there are a lot of combos you can make work.
AoE Azerite Traits
For AoE just make sure you have these 2 traits, the rest should be single target traits that are available.