Can't really speak to the L-N or Diefenbach.
My Sjoberg Elite 8' bench has been something of a disappointment.
-The top shrank, but since the end cap is bolted on, the shrinking top eventually started to split. Time will tell what happens there.
-The top also bowed a bit, it's crowned along its length. A 4' ruler from HD has somewhere between 1/8" and 1/4" under each end of it.
-The optional cabinet kit... I've seen better stuff come out of lesser pre-fab shops. The drawer sides on the top drawers were cut too wide, and they rub on the inside of the box, eventually causing one of the drawer fronts to pull off.
-Shipping... leave it to Woodcraft to screw this one up. First one, they must have had monkeys loading, and driving the truck... the vises were both beaten to crap, and the box was half destroyed. Hadn't even loaded the thing on a pallet, just tossed it in with everything else. Second one wasn't as bad, but the end vise was still damaged. Functional, but damaged.
For the price of this bench, I expected a lot better.
Current plan is to give it a new lease on life, plane the top down flat, and try adding a new front vise. Maybe make a new box of drawers for it, too. But that's a lot of work for a bench that costs what this one does.
Do I want to sell it? There was a time. It's settled into a pretty solid thing to work on, it's just not flat enough to clamp or laminate on, and the cabinet thing is junk.