After looking at the specs of both tractors, there is no contest. The MT573CPS would win it hands down.
Disclaimer: I have never seen one of these two tractors in person, ever. I am simply looking at the specs on both tractor data and ls usa.
The MT573CPS compared to the XU6168CPS things I looked at:
Engine: they both have the same engine: The LS L4C25-T with different HP ratings, probably due to different turbo sizes and/or ECU programing.
The MT5 has more gears: F20-R20 vs F16-R16
The MT5 has much better hydraulics than the XU: 19.8gpm vs 14.5 which directly translates into better lifting capacities
The MT5 has 6,614bls of lifting force at the 3-point vs 4,079lbs for the XU.
The MT5 also boasts a slightly larger tire size 16.9 – 30 vs 16.9 – 24 for the XU
And lastly the MT5 is over a thousand pounds heavier than the XU. This is likely because its physically larger, slightly, than the the XU. I prefer a heavier tractor over a lighter one.
This is not to say that the XU is not a capable tractor. But if I was shopping for this size with these features, the MT5 is where I'd put my money, if money was no object. Of course, I'd do much more research and attempt to find these tractors for a test drive before buying.