Undoubetly the strongest among Ravana,’ s sons with or without boons. He was a master of scorcery and black magic. Defeated and captured Indra in battle. .No one can defeat Indrajeet once he finishes Nikumbhala sacrifice as per Brahma,’ s boon. Killed 67 crore vanaras using Brahmashirastra and knocked out the entire vanara army including Rama and Lakshmana unconscious. Converted sons of Kadru into infalliable arrows using dark magic and knocked out both Rama and Lakshmana. During final battle of Indrajeet and Lakshmana Indrajit used no boon or infalliable weapon yet both of them were equal on archery.
2.) Atikaya- He was unkillable fo divine beings due to Brahma,’ s boon and recieved a Brahma armour which could be pierced only by Brahmastra. Using normal arrows Atikaya countered Vajra of Indra and Varunpash of Varun dev which was capable of defeating Death itself in battle. Wrecked havoc in the vanara army using his weapons. Fought a terrific battle with Lakshmana and even swooned him with a snake arrow.
3.) Akshay Kumara
The reason for placing him on third is he gave a tough fight to Hanuman. He managed to make Hanuman bleed with three arrows and gave a very fierce fight even though Hanuman was not using his full potential. Even the gods and sages applauded his powress.
Oozing the blood from his wound caused by those arrows descended into his head (by Aksha), looking like the newly risen sun, his eyes bathed in blood rolling rapidly, Hanuma shone brightly like the sun surrounded by a circle of rays, having the arrows as its rays.
That valiant Hanuma, whose swiftness was equal to the mind and possessing impetuous valour in battle, rushing forth like wind in the space between one arrow and another and thus escaping Aksha's arrows, moved in the path visited by wind (the sky).
He was finally killed by Hanuman when the latter took him seriously.
4.) Trishara
He countered the peak of tree hurled by Angada at Devatanka and overpowered him in battle. Countered almost everything hurled at him by Hanuman. He was finally killed by Hanuman after a fierce fight.
5.) Devatanka- He overpowered Angada in battle with help of Trishara and Mahodra. Finally Hanuman killed him.
6.) Naratanka- Defeated the vanara army using a single spear. Angad had to arrive to stop him from destroying the vanara army. Made Angada unconscious with a single punch thus showing his immense physical strength.