A friend of ours on VG deals with high end villa clients and she has told me some real horror stories about Dolphin. In one instance "Dolphin Greg" actually made threats to withhold service if any guest submitted a negative review online.
We have used all of them and have been the happiest with Chillout. We had a negative experience with Island Time substituting a really crappy boat for a crossing in swells we never should have crossed in. We were never told in advance nor compensated and I was actually sick on arrival. I know they consistently get great reviews but that just left a bad taste in my mouth. I would use them again in a pinch but will always choose Chillout first.
Chillouts Midnight Express boats are incredibly comfortable and fast.