In terms of her essay writing, "A room of one's own"[2] is probably most famous/influential, although from a personal perspective I didn't find it as enjoyable to read as Mrs Dalloway. In general I prefer novels to essays so take that however you like.
[1] Btw my recommendation is don't read anything about it beforehand. Synopses/cliff notes/the wikipedia entry will probably ruin the experience for you. The book is about really getting inside the head of certain characters and understanding their thoughts and motivations. If that sounds interesting to you, then that's all you need to know to dive in.
[2] https://victorianpersistence.wordpress.com/wp-content/upload...