It's an interesting question. Generally they mean "cheese". They're used in different Chinese spoken areas, but sometimes it doesn't always mean "cheese" in some areas. Coco's answer is also correct, it just depends on where you live. In Taiwan both 芝士 & 乳酪 mean cheese. But 奶酪 doesn't, it means a dessert called "panna cotta". Here is the picture: (http://3.bp.blogspot.com/_Z-XA7IBq3kE/S9r3lykrlrI/AAAAAAAAACA/_lBi-AFJ0D8/s1600/%E5%A5%B6%E9%85%AA%EF%BC%88NEW%EF%BC%89.jpg)

For all I know ,奶酪and 芝士are the same ,mean "cheese",just transliteration.乳酪means "cheese,cream,creme or knish".I hope this has been of some help!

"芝士"is a little bit like the transliteration of "cheeze", if you read it you will find its sound is similar to "cheeze", right? So maybe you can see sometimes it is also called "起司" in some bakery or restaurant, its the same reason. I think its more popular used in the south China, where people like to use the transliteration when dealing with foreign languages, for exemple, if you go to Hongkong or Canton, you will find some grocery shops use "士多" (shì duō) instead of "商店＂, like "XXX士多＂=＂XXX商店＂, because "士多＂'s pronunciation is similar to "store", I found it very interesting when I first visited HK. Hope can help you!

thank you very much! :)

芝士 = is very rarely used 奶酪 = solid cheese 乳酪 = soft as cottage curd