I've ridden on both of NCL's modern 77,000 tons ships servicing North America recently.
I liked both the Sun and the Spirit a lot.
There are some things which are better on either ship, and other things are about the same.
Individual Staterooms choices, decor and layout is better on the Sun, although the Spirit has better bathroom layouts. The Spirit's glass door to the shower is much better than the Sun's curtain. But the Sun has mini-suites and three levels of suites fore and aft while the Spirit doesn't have mini-suites, and just one level of suites fore and aft. If you desire luxury, there's more choices on the Sun.
Elevator arrangements and the atrium area is better on the Spirit. Swimming pool areas are better on the Spirit. Kids areas are better on the Spirit. The Spirit has a jogging deck topside, while on the Sun you must jog on the Promenade Deck that's also full of strolling passengers. The Spirit is overall easier to navigate from fore to aft than the Sun. There's one half deck aboard the Sun one must climb up a deck to access any elevators.
Generally, restaurants and lounges are about the same. The Sun has a better Italian restaurant than the Spirit, but you have to pay a surcharge to eat at the Sun's Italian restaurant, while on the Spirit it's free.
Both ships have an Observation Lounge above the Bridge area, which is called the Galaxy of the Stars on the Spirit. The Sun's has an open balcony in front of the Lounge while the Spirit doesn't. But the Spirit's Galaxy of the Stars has a navigation control computer display, and an overlook area where you can see along the entire side of the ship that the Sun don't have.
Never-the-less, as you can see, I would recommend sailing on either ship. Both ships offer a full assortment of activities and facilities that NCL uses on all their ships.
I haven't address your questions about specific ports intentionally because I haven't sailed to either before.
If you do select the Spirit, a must do activity aboard is to check out the Bridge Observatory under the Galaxy of the Stars.