Lingqi, preferably red, then orange, and finally purple.

When the weapon is full, it will increase its combat power by about 25-30w.

Don't sell extra purple eggs. Later upgrades are very useful. Note that the probability of upgrading is virtual, and there is no difference between 20% and 80%. It is better to improve 100% after level 80. If 90% fails, 45 eggs will be lost. Might as well bet on 20% promotion.