I was thinking of Southern Similan, there are a large number of liveaboards to choose from and they offer more diving per day than you'll get by staying on land.
I think I may have painted a slightly poor picture of the Northern sites, they can be tougher sites to dive but most of the tour leaders will avoid the peak current times whenever possible.
It's really up to you and your partner, a risk free trip to the South or include the North with what I think is one of the best in Thailand (Richelieu Rock). The northern sites will still be there next time.
Nothing wrong with the diving around Phi-Phi and Phuket either, but you will have better visibility at Similan.
I think I may have painted a slightly poor picture of the Northern sites, they can be tougher sites to dive but most of the tour leaders will avoid the peak current times whenever possible.
It's really up to you and your partner, a risk free trip to the South or include the North with what I think is one of the best in Thailand (Richelieu Rock). The northern sites will still be there next time.
Nothing wrong with the diving around Phi-Phi and Phuket either, but you will have better visibility at Similan.