“Most nasal” is vague. The highest number of phonemic nasal consonants/vowels? With the highest frequency in actual use? Nonphonemic?
Yanyuwa is highly unusual in that it has a seven-way distinction between [m], [n̪], [n], [ɳ], [ṉ] (palato-alveolar), [ŋ̟] (front velar), and [ŋ̠] (back velar). This may be the only language in existence that contrasts nasals at seven distinct points of articulation.
These languages use phonemic nasal vowels:
[…] Paicî (an unusually large number of nasal vowels)