I went out with the Viking on two trips, and having done several liveaboards including aggressors, I must say it is an excellent boat and staff. In fact I go out with them again on a 10 day trip to Similan/Burma in April. Yes, it is not cheap compared to other Phuket-based liveaboard. And yes, it is spacious, with very nice working facilities. It is not yet finished though. Many more amenities, as well as nitrox, will be installed. 20 years ago when I was a backpacker I would have picked another boat. Today, taking pictures and preferring to have my own shower, I would certainly go with them again. So, I can only recommend the Viking. They do PADI courses for free which is another BIG plus for you who would like to learn more. The staff is very safety concerned, and the boat is equipped accordingly.
Thomas