What´s the best covenant for Flag Carry in RBG in your opinion?

[Becket]

I just can´t decide

[Lodravel]

I prefer NF. Heard some mention Necro to be their favorite, but I perceive the added speed to make it superior to the alternatives. You can pull of some crazy fast flag caps if you don't get too cocky with it.

Convoke is also quite decent but getting it off is a pipe dream in most situations.

[xtramuscle]

Kyrian is pretty good aswell with cd reduction on barkskin and SI

[wing5wong]

Played both NF and Necro to 2500+ as boomy and guardian.

Necro is for sure weaker if you ever intend to play boomy, but is a fantastically strong FC. Sulfuric Emission with Emeni Soulbind can be a lifesaver in tight situations..
NF is much more mobile with soulshape and affords you the option of moonkin convoke (and flap), though i found myself playing resto affinity in 99% of situations.

Hard to say which is best, it depends on how your team and yourself play, as well as what the other team is doing.

[Aedruid]

You make a good point, having that necro shield as a flag carrier will be a life saver when a rogue stuns / pops their cds on you.