The XR does boast a bit more power. That's very important for safety reasons given how this rideable keeps itself up. The + is slightly lighter and thinner. The difference is small on both accounts but for the purpose of doing certain tricks, I've found it slightly better than the XR. Even "slightly" can make massive differences in certain situations. I'm sure most of us realize it but some don't; there are two different types of flatland 180s. The + will allow you to enter the easier one at a lower speed because it is thinner and your float plate will be further from the ground. It was slightly aggravating making the transition to the XR on that front but you get used to it. As for the harder 180, the board is 2 pounds lighter if memory serves. The difference there is barely noticeable. Due to the fact that it is thinner, you will also be able to climb certain features more easily and you will be able to get your nose over slightly taller objects. Also, the + seems to be able to purposefully drag tail a little better.
If, and I can only imagine if, you were going to only use it for short range/tricks only, I'd definitely have to say the plus over XR, in my opinion. Alot of that has to do with the specific tricks that I do personally. Even then, in my eyes, none of that really compares to not having to worry about range anymore. If you have both, don't gut one. Enjoy riding both for their strong points.
