Essentially, the VYPR is the simplest handguard we carry. It provides the most options for mounting accessories, and it the lightest rail we offer. The RPTR is the heaviest rail we sell but it gives you the added benefit of integrated picatinny rail sections on the front. This allows you to mount lights, bipods, etc... without having to buy any extra picatinny rail section attachments. The HWK rail is the best of both worlds. It is almost as light as the VYPR and also has an added picatinny rail at the bottom for mounting a bipod or other accessories.
We also have a really helpful quiz you can take to find the perfect handguard for your build. Check it out!: https://www.stngrusa.com/handguard-quiz/