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.
Apple replaced 3D Touch with Haptic Touch on the iPhone XR and it looks like it will extended to the larger OLED models in 2019.
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.