Go hard - Trinidad SR. We have been cruising in S and W Pacific for ... hmmm, almost 13 years now. Our first batch of Trinidad SR lasted 3 years; we are only now getting around to redo-ing batch #2, four years after it was applied. The bottom gets regular, vigorous scrubbing yet the paint
keeps sticking and working. We hauled out 2 weeks ago -- bottom was so clean we didn't even bother power-washing.
The problem -- ya gotta get the paint in your hemisphere. Pettit's licensee in this part of the world, Altex Paints (AUS & NZ), can't manufacture or sell Trinidad due to a fussy regulatory problem. The only way to buy it in Oceania is to have the great luck of finding some that snuck out to a retailer before the regulatory embargo was imposed.
If Trinidad isn't available, I would go (am going) with Ultra.