I got the 3102 on my XU6168. Very happy so far. It’s very solid with the subframe mount. It will pick up the rear of the tractor with loaded rear tires without breaking a sweat.
You’ll need to buy or make some feet for the stabilizers. LS doesn’t provide them or even sell them last I checked. There are a few threads on where to acquire them though.
My tractor originally came with a LB2105. I thought it was pretty wimpy. I had originally asked the dealer for the larger backhoe, but was told it wasn't available for my model. I was so dissatisfied with the LB2105, I contacted LS tractor directly to ask about the bigger option and was told it was available. The brochure only lists the smaller option, but the LS website showed the two choices. The dealer agreed to swap out the backhoes for the difference in price, $800 more for an LB3104. I think the smaller backhoe would be fine where you have normal dirt. In the Rocky Mountains, not so much. I'm much happier with the LB3104 and definitely noticed a difference in power.
One caveat, due to an engineering design flaw, the LB3104 seat hit the rear window of my cab. I had to move it forward by two mounting holes to clear the cab window, but now the leg room is minimal. If you don't have a cab, it shouldn't be a problem.