I don't know about best but Camellia and Moonvine are solid RG Knights who don't have crit bonuses. Camellia adds a decent chunk of +attack for the whole squad, 30% immediately and 35% per turn up to a max of 70% on top of that. Cammy also has the standard dodge tank staples (+defense, 80/50 evasion, 425% counters that can trigger super-counters due to the defense buff). Moonvine works well in solar teams due to +25% shine crystal drop rate, +70% solar damage, and +40-80% attack power based on solar bursts used along with 1.2x skill proc.
Checking the wiki, Heliopsis is sort of a defensive Moonvine with +15/30/45% defense based on solar bursts but she gets some offensive bonuses as well like skill proc/damage buffs.