Love it or Hate it. but Hashirama is the strongest not genetically modified Ninja in whole Naruto series.
Madara used his brothers eye to get EMS and later implanted Hashi's DNA to get rinnegan at old age.
Obito was shit but thanks to Hashi's Cell , he survived and had enormous stamina due to hashi cell. Obito even dont need to eat food due to hashi's cell . :D
Naruto would had been a normal kid by natural birth but kyubi was sealed in his body , and that was source of naruto's power.Kyubi was not naruto's body part.
Sasuke was modified with Orochimaru's cursed marked. later He got an eye transplant otherwise he would had been blind.
Orochimaru and Kabuto are the worst in this catagory because there whole body was genetically modified hundreds of times. :D
Hence Hashirama is the true original ninja in the manga. closely followed by Minato and Tobirama.