Comparing Avraham and Noach

Given their close proximity to one another in the Torah and their loyalty to Hashem, it is understandable that Chazal, through Midrashim, compare Noach and Avraham to one another. The most well known comparison is mentioned by Rashi in the beginning of Parshat Noach (Breishit 6:9). The Torah writes that Noach was a tzaddik, a righteous man, in his generation. Picking up on the words "in his generation," Rashi cites a debate that is found in the Midrash:

יש מרבותינו דורשים אותו לשבח, כל שכן שאלו היה בדור צדיקים היה צדיק יותר, ויש שדורשים אותו לגנאי, לפי דורו היה צדיק, ואלו היה בדורו של אברהם לא היה נחשב לכלום
Some of the sages interpret it (the phrase 'in his generation'), favorably: How much more so if he had lived in a generation of righteous people, he would have been even more righteous. Others interpret it derogatorily: In comparison with his generation he was righteous, but if he had been in Abraham’s generation, he would not have been considered of any importance.

Those who viewed Noach as a tzaddik who would have transcended generations believed that had he lived during a time period other than that of the evil generation of the Flood, he would have flourished even more. On the other hand, those who claim that Noach "would not have been considered of any importance" in Avraham's generation believe that Noach's righteousness was relative; he was righteous, but look at the people around him - had he lived at a time when the rest of humanity possessed the least bit of morality and integrity he would not have stood out like he did in his generation.
While the debate over the transcendence of Noach's righteousness is left unresolved, the Zohar cites another difference between Noach and Avraham, which seems to indicate that Noach's righteousness was relative. The Zohar writes,

“

ויגש אברהם ויאמר: האף תפסה צדיק עם רשע” (בראשית יח,כג) - אמר ר’ יהודה: מאן חמא אבא דרחמנותא כאברהם? תא חזי: בנח כתיב (ו,יג-יד): “ויאמר אלוקים לנח: קץ כל בשר בא לפני... והנני משחיתם את הארץ. עשה לך תבת עצי גפר...” ואשתיק ולא אמר לו מידי ולא בעי רחמי. אבל אברהם, בשעתא דאמר ליה קב”ה: “זעקת סדום ועמורה כי רבה וחטאתם כי כבדה מאד. ארדה נא ואראה...” - מיד כתיב: ויגש אברהם ויאמר: האף תפסה צדיק עם רשע
'And Abraham drew near and said, will You also destroy the righteous with the wicked? (Breishit 18:23) - said Rabbi Yehuda: Who has seen a father as compassionate as Avraham? Come and see: Regarding Noach it is stated (6:13) 'and God said to Noach, the end of all flesh is come before me;...and behold I will destroy them from the earth. Make an ark of gopher wood...' And Noach held his peace and said nothing, neither did he intercede. Whereas Avraham, as soon as the Holy One blessed be He said to him: 'Because the cry of Sodom and Gomorrah is great, and because their sin is very grievous. I will go down and see...' Immediately, as it is stated, 'And Abraham drew near and said: Will you destroy the righteous with the wicked?'

When Hashem told Noach that He was going to destroy the world and that he should build an ark to save himself and his family, Noach obediently listened. He was a tzaddik and was worthy of being saved. However, according to the Zohar, Avraham was greater because when informed that Sodom was going to be destroyed he challenged Hashem in the hopes that he would be able to save the residents of Sodom and Gomorrah.
In the words of Nechama Leibowitz (Iyunim L'Sefer Breishit pp. 46),

נח אינו ערב לאנושות, נח אין בו אחריות לעולם כולו, נח הוא מאלה הניצולים אשר את נפשם הצילו. והעולם - יחרב. והוא נחרב. “צדיק תמים?” כן, בדורותיו.
Noach a guarantor of mankind, Noach does not have a responsibility to the world as a whole. Noach belonged to those who were satisfied to save their own souls, while the world is destroyed. [He was] 'a perfect tzaddik?' Yes, but only in his generation.