It is Act II scene 3 that clearly shows with whom Malvolio is in conflict in this excellent Shakespearian comedy. Note how, when Malvolio interrupts the late night festivities organised by Sir Toby Belch, he is harsh in his condemnation of such activities:
My masters, are you mad? Or what are you? Have you no wit, manners, nor honesty but to gabble like tinkers at this time of night? Do you make an alehouse of my lady's house that ye squeak out your coziers' catches without any mitigation or remorse of voice? Is there no respect of place, persons, nor time in you?
It is important to realise that the play's title, Twelfth Night, refers to a festival which is not celebrated any more, but which represented the last celebrations of Christmas before the long, hard winter months ahead, characterised by Lent (a time of fasting). Traditionally, Christmas decorations are taken down on Twelfth Night to indicate this. In the play, it appears that Sir Toby Belch represents the true party spirit of Christmas that will not yield, whereas Malvolio, described as a "Puritan," represents sobriety, seriousness and duty. Note how, in response to Malvolio's words, Sir Toby Belch responds as follows:
Dost thou think, because thou art virtuous, there shall be no more cakes and ale?
This appears to be the central conflict concerning Malvolio: he is set against Sir Toby Belch and represents order, duty and denial, whereas Sir Toby quite clearly represents excess and chaos.