I would take the long flight. Suites on 777 are almost indistinguishable from those on the A380. The only difference is the shower. Also, business class on the A380 is better than business on the 777 , so upgrading the journey on the 777 leaves you with the nicer business on A380

The minuses of upgrading the long flight are
No 1st class lounge access in Dubai
No onboard shower

Overall I would prefer the 14 hours in higher comfort than those 2