This is just my opinion as a vaiShNava, no more no less. I do not speak for all vaiShNava-s or bhAgavata-s, let alone all Hindus. However, in my honest opinion, Jesus was not realized and he and his disciple paul were to the contrary bhaktadveShI-s who resented devotion and mocked actions similar to that of taking prasAdam ("Howbeit there is not in every man that knowledge: for some with conscience of the idol unto this hour eat it as a thing offered unto an idol; and their conscience being weak is defiled". -1 Corinthians 8:7). To consider him (Jesus) an avatAra of bhagavAn would be somewhat blasphemous from my perspective. Some of the material he preached may have been in accord with the shAstra-s, some of it may not have been. However, a hater of devotion to shrI nArAyaNa (like Jesus was) is not even on par with an exceptional devotee, let alone bhagavAn himself. shrI kR^iShNa states in the gItA that he is dear to his devotees regardless of his/her/its standing, a sort of ambivalence (udAsInavadAsInamasaktam, lit. indifferently situated and unattached); this means that even a tree who has devotional tendencies and acknolwedges some degree of dependence on bhagavAn is greater than a human that considers himself to be supreme (like Jesus). Even shiva/rudra, the greatest of the deva-s and sarveshvaraH (the lord of all), emerges from nArAyaNa/mahAviShNu/kR^iShNa. Worship and adoration of shrI kR^iShNa is also the eventual object of meditation and j~nAna yogam, and this is futher substantiated by shrI madhvAchArya's quote from the varAhapurANam of shrIvedavyAsa, when he states "mukhyaM cha sarvavedAnAM tAtparyaM shrIpateH param utkarShe tu tadanyatra tAtparyaM syAt avAntaram," which indicates that the main purport (mukhya tAtparyam) of all the veda-s (sarvavedAnAM) is that the husband of shrI/lakShmI (shrIpateH) is supreme (param).
TL DR version: I personally don't think Jesus was the supreme lord (which would be necessary if one is truly an avatAra of viShNu bhagavAn).
Edit: Oh yes, and regarding gautama buddha I do believe that he was an avatAra (not the ninth of the dashAvatAra like some Hindu-s believe, but nonetheless an avatAra). The same applies to the founder of jaina dharma, R^iShabha. This is because of the reason mentioned above by aupamanyava (i.e. based on the pramANa of the bhAgavatam). I can't say about other revered figures like the later jaina tIrtha~Nkara-s such mahAvIra, neminAtha, etc. or revered bauddha figures like shAnavAsa, k****igarbha, nAgArjuna, avalokiteshvara, ma~njushrI, padmasambhava, etc., perhaps or perhaps not.