Opus -- I think the verdict is that DL's Business is way better than UA's, BUT if you can upgrade to UA's First Class, then that's your best bet. Have you sat in UA's new "First Suite" seat? It really blows all of the other options out of the water.
However, if you're gonna be in Business, I would gladly take the connection at LAX, and get the far-superior DL product.
Just MHO.