Rome: priority check in, board in, and security for originating flights very well shown and implemented. No priority channel that I could see for transfers though (although in fairness it went faster without one than typical skypriority/acces no1 transfer elsewhere so maybe they only do it at peak times?)

Nice: priority check in and boarding perfectly marked and implemented but no fast track security for regular sky priority (only the airport card) and no fast track emigration/immigration, which is a pain in the back when many terminal 2 non-Schengen flights leave around the same time (we had JFK, SVO, TUN, TLV etc all within a few minutes) especially as, as is typical in France, EU/non-EU lines are neither respected nor implemented (as is typical in France too, signage for EU/non-EU is not clear enough and people can 'pretend' they did not know).

JFK: T2/T3 great. DL's concept of a separate terminal for Skypriority check in is probably the best I can think of. Great implementation of priority boarding too. However, no fast track immigration.

T1: Not so great. Priority check in works well (I found the AZ version more clearly signed than AF and KE's), fast track security poorly implemented (although signed). Priority boarding very efficient (see below) for AZ. Again no fast track immigration.

Note: on my recent flights both DL and AZ had people effectively checking individual boarding passes of people who were queuing in the Sky Priority lane and sending "mistaken" passengers back to the long line. It makes a real difference and I think is good practice.