I've sailed suites on
DCL, Celebrity, and HAL - well technically Premier also, but since they are no longer in service, I'll leave them out. LOL!!! I've always only sailed in suites, until 2011 when I decided I would no longer sail in a suite on DCL, since their suite perks were not worth the additional money. They really didn't compare to what the other lines did. I broke that by sailing in the Walt suite on the Magic in 2013, because my sister wanted to, but other than that I stick to 4A on DCL.
They all have priority boarding and priority tendering so I'll leave those out. On DCL you can sail in 2 staterooms and get
Castaway Cay loyalty points for both staterooms, but if you sail in a suite you still only get one credit, even though it is like booking multiple rooms. Other cruise lines gives credit for suites. On DCL I had sailed almost 40 days in mostly suites and still was the same level as a single room 3 day.
Celebrity we had a butler that took care of everything, he brought us goodies every afternoon, planned a party, they fully stocked a fridge with drinks (including alcohol), offered to help with unpacking, had a computer with internet in the room (this was their penthouse) hot tub and treadmill on the deck, reserved the special wine room in the specialty restaurant for us, etc.
HAL has the Neptune lounge, with a concierge desk always manned, they've always been so helpful. They will even arrange afternoon tea service in your stateroom or course by course dinner. The lounge has goodies throughout the day, tables for visiting, games, etc. Champagne and fresh fruit in the suite, corsages on formal night left in the room, free laundry (my personal favorite).
Don't get me wrong, I love the concierge on DCL - they've always been great, but I can attest to the fact that other lines are great also.