I just came back from diving in Khao Lak with Wet Zone Divers. They have a brand new speedboat they use for day trips to Koh Tachai, Koh Bon, and Richelieu Rock. Two dives per day. Leave 7:45, back by 3:30. They have a good, well-run operation
You're getting to the end of the season, so what @stevenl said (liveaboard being a more stable platform) might be good advice. I can't speak to that personally.
As for bang for the buck, the dives were not cheap.
Anyway, if you decide to do day dives from a speedboat, Wet Zone Divers is likely the best option. In fact, I was recommended to go with them by another company who did not get a referral.
Hope that helps.
You're getting to the end of the season, so what @stevenl said (liveaboard being a more stable platform) might be good advice. I can't speak to that personally.
As for bang for the buck, the dives were not cheap.
Anyway, if you decide to do day dives from a speedboat, Wet Zone Divers is likely the best option. In fact, I was recommended to go with them by another company who did not get a referral.
Hope that helps.