Which one you choose depends on what you’re looking for. BB cream and foundation are similar in the sense that they both even your complexion, but there are differences between them. BB cream has a lighter texture and can be more hydrating for your skin and offers SPF protection, unlike many foundations. However, foundation can offer extra coverage and there is usually a broader range of shades to choose from so you could be more likely to find your exact match.
But remember, it doesn’t need to be a straight choice when it comes to BB and foundation; you can use both by applying BB cream first and your foundation on top.