Hey there:
First, I did not know JD made a residential lawn tractor with a locking differential - news to me. I bought their X-370 a couple years ago (great machine) and had to buy a couple 45 lb. weights to achieve necessary traction to mow my extremely hilly field adjacent to my lawn. I don't think JD had a locking diff. then, or I would have sprung for it.
My X-370 replaced a Husky LT42DXLS that did have the locking differential, and was a great mower that would climb a tree. But (and you can refer to my earlier posts for more details), the tranny fell out on the ground twice in 2 years. It was fixable both times, but I grew uneasy with it, afraid it would continue to happen. You will find, if you research it, the Husky you are considering has experienced the same tranny brackets cracking problem I did. Also, one of the scalping wheel brackets bent over time. So much so that I had to replace one. Bottom line: great mower, wimpy steel! I sold it to my neighbor and was glad to see it go. I don't know, but I suspect the TS348XD is a newer version of what I had - hopefully beefier! I will not buy a Husky again, but at 74 I may not ever need to replace my JD X-370 - which with the hydraulic power steering and deck lift, extra weight and extremely serviceable tranny, I love. If you ever have a mower with power steering, you'll never go back.
Likewise, Cub Cadet - several years ago I bought one new (don't remember the model #) from a CC dealer, and it was a POS. Used oil, had to replace the leaking gas tank under warranty and the first mow the left front wheel fell off. Also, the guy didn't tell me the tires were WAY over-filled. I wondered why it rode so rough
! The oil burning never stopped. I sold it to a friend of my son with full disclosure of its issues.
I don't know what JD model you're considering or the price, but that would be my choice - based upon only MY experiences with the ones I've owned. Good luck