raviepoo - also "heard that they monopolize moorings put in by other operators" is hearsay i.e. not particularly reliable and I seriously doubt that it is true. Each of the boats moors to a single site for two dives and perhaps a night dive and then moves to another site - many times we were diving within sight of both PH and A boats arriving when they were already tied up - they are faster after all - with others tied to mooring bouys beyond them. This does not ring true to me. Needs something more to back it up to be credible.
You are absolutley entitled to your opinion, and I can see how the PH and A boats are more attractive for some. But from personal experience I would give the Nekton boats an A+ rating. If you want the "Yacht" feel and the "luxurious touches" by all means go with them, the trip will be great and you will get those things - you won't get them on a Nekton boat. Otherwise you get exactly the same thing on a much more stable boat (which is really important for some of us), the same great service, more space to play in, not as good food for less $ on a boat that was designed for diving not a retrofitted yacht, but is really really ugly on the outside. (looks like a oil drilling platform at first glance)