We've booked signature many times. It is my first choice if it's available at the right price. It's true that skyservice is crap, but it's usually a short flight and then you're there.
In my opinion signature has the best reps at the resort. We always pick up our tickets at the airport and with signature there has never been a delay or a problem.
My second choice is Sunwing, and my last choice is Sunquest. Too many problems with sunquest, bad reps at the resort, bad customer service at the airport and delayed flights.