In Christianity it is often said that Gamliel was the greatest rabbi of all time. But it seems that he is just being hyped because according to Acts he trained Paul. Do Jews really view him as a great rabbi? I've read a little bit of the Mishnah, so I've seen the story about how he teaches his disciples that one is not to say the Shema on his wedding night. Yet his disciples heard that on one of his wedding nights he did say the Shema so they questioned him on it. And his reply “I am not like other men.” He teaches his disciples that it is a sin to morn the death of a slave, and then when his slave dies, he mourns, and his disciples question him on it, and his answer is “My slave is not like other slaves.” Etc. Basically, the rules he makes apply to everyone but himself. He seems to be presented more as a big hypocrite than a great rabbi.
Rabbi Gamliel was not the best rabbi of all time. I do not know of any Rabbi who has ever been given that title, except from sub sects of Judaism who might venerate one Rabbi over another. Many Rabbis are given pinnacle accolades, declaring that without them the nation would be lost, or after them there was a great reduction of some kind.
However, being the Nasi of the Sanhederin, Rabbi Gamliel was the post powerful Rabbi while he was Nasi. In fact, there is even a roman law, which says it is forbidden to insult and denegrate the "Nasi" of the Jewish people. (From the book Encylopedia of Talmudic Sages)
However, there were 7 Rabbi Gamliels.
The greatest Rabbi of all time was Moshe Rabbeinu.
He is recognised in the Torah as being the greatest prophet ever, but is also recognised as the authoritative Rabbi.
He taught the entire Torah to Joshua and it was passed on.
Source: first mishnah of Avot.
And as we know, every subsequent generation is one further away from Moshe Rabbeinu which is why we consider earlier generations to have greater Torah knowledge than the later ones.
Rabban Gamliel is a Rabbi and Nasi in the generation of the written version of the Mishnah. The Mishnah was the oral law passed down through generations and was not written down until later.
Therefore with regards to the written version of the Mishnah, Rabban Gamliel is a head figure. He was descended from Hillel the elder who learned everything he knew from Avtalyon and Sh'emayah.