If I were you, unless you're plan to be a collect, get the v4.5. From what I've heard, it's pretty much the same thing though there's more super awesome characters and different items.
If you are planning to be one of those collectors that's like "IMUSTHAVEALL" then get a v4 if you can find it because they'll be pulled of the shelves soon if they aren't all ready. You'll still have a little more time to get the v4.5 if you plan on getting 'em all.