Vxr is a simple carby system, vxri is EFi engine which is said to be very efficient than Vxr (i-e non-EFi) while vxl is again non-EFi carby system BUT HAS some power features like power windows and power steering, while vxli is the same as vxl but it is EFi system.
Ive no idea about their mileages, experts can guide you about the mileage part but yes VXLI has discontinued only VXRI is available and whatever model you get go for an EFi engine model it will give you better mileage.