Don't Wait If You Love 3D Touch
If you really love Apple's 3D Touch, you'll probably want to start looking at the current lineup of iPhones.
Instead, the new iPhones are expected to have Haptic Touch which works in fewer places than 3D Touch. Examples include the lack of support for Quick Actions app menus and the Peek and Pop feature for previewing content.
According to 9to5Mac, the new iPhones will feature a new engine that's codenamed "leap haptics" behind the scenes. It's unclear what will be different.
If you love 3D Touch or think you might use it, you might want to start looking at the iPhone XS, iPhone XS Max, or an older iPhone model.