It really depends on what kind of stories you want to read. Do you prefer old comics or would you like to read something a bit more modern? My general advice to new readers is to start with something modern. Old comics are exceptionally funny and you can find many over-dramatic great lines in them, like “The Scarlet Witch is free… and angry! And unlike your bride, Ultron, the Scarlet Witch can hurt you!” (The Avengers #171), they also have interesting stories and concepts, but… they can be a little overwhelming for new fans. They could be a bit silly – and that’s something I’ve personally enjoyed, but it’s not a great introduction to the characters. Another big problem is that most of those stories have not been published recently, so it’s hard to buy them.
Anyway, if you still want to try something classic, you can start with:
Avengers: Kree/Skrull War, (amazon) collecting Avengers #89-97. It’s a famous marvel event from the early 70s, it features many characters and it’ll give you a good idea of what old comics are about. You’ll get a look at 70s Wanda and you will decide if you want to read more about her. If you do, you can continue with:
Essential Avengers 5, (amazon) collection Avengers #98-119. It’s actually a great, great read for Wanda fans, since it focuses on her blooming romance with the android Vision, on how that affects her relationship with her brother and how the society felt about a relationship between a mutant and an android. The essential collections are cheap, compared to most comics, because they are printed in black and white. That’s a good deal, since the art in the 70s comics doesn’t gain that much from coloring, but it can be really beautiful in black and white. If you like this collection, you can move to Essential Avengers 6 and so on. There are some great stories later on, but that’s a good start-point, at least in my opinion.
But, as I said, I’d advise you to start with something more recent. And this brings me to my all-time favorite Wanda/Avengers series:
The Avengers (vol 3) by Kurt Busiek. Busiek’s run lasted for 55 issues and what he did with those characters was completely amazing. Wanda is one of his main players, if not the main player. The series has recently been collected into 5 big paperbacks with the title Avengers Assemble, you can find them all on amazon:
This is a really great epic collection. It feels like a classic Avengers comics from the old times, but it doesn’t sound outdated or anything. Busiek works great with the characters and brings out the best of everyone. Wanda is notably not the only female Avenger here, Busiek wrote great arcs for Carol Danvers (Ms. Marvel), Firestar and Silverclaw, you also get nice appearances by Wasp and She-Hulk. The final arc in this series – Kang Dynasty – is probably my favorite comic story ever published. So yeah, you get that I’m not really objective here :D But it’s a good title, I swear!
Things are trickier after that. You can check out Avengers Disassembled (amazon) which is all about Wanda doing psychotic stuff and as I fan of the character I’m torn about the whole thing. It requires knowledge to some of her previous stories, mainly this one, but Wikipedia can fill you in, when you get there.
After that you can move to the big event House of M (amazon) , which I actually like. It’s a great read, but sadly it resulted in Wanda disappearing from comics for nearly a decade.
Her return, however, was wonderful, at least for me. It happened in Avengers: The Children’s Crusade (amazon), but in order to get to that, you should read Young Avengers by Allan Heinberg (amazon). That Young Avengers collection doesn’t future Wanda (with the exception of two glorious pages), but it’s a great, great read, one of the best you could ever find. And in it you’ll find a young gay boy with powers, similar to Wanda’s, who is trying to figure out if he’s one of her lost twins. The story continues in Avengers: The Children’s Crusade, Wanda returns to Marvel comics and it’s all wonderful and I’m puking rainbows when I’m just thinking about it.
So, that’s my recommendation! Of course many people may recommend you some different stories and different arcs. I’m not saying that these are, without a doubt, the best places to start. But these are my favorite stories and I can’t help praising them when someone asks :)