I have Micron Optima on mine - I chose an eroding antifoul as I don't like the idea of paint buildup. It's waterbased which makes it dead easy to apply and clean up afterwards. It is incredibly soft (like kiddie's poster paint), you can literally 'sand it down' with a sponge!! It does work very well on the under-hull surfaces if you use the boat regularly, but you need at least 4 coats to start with. It is not the right thing to use on the transom or waterline though, as these areas need scrubbing (no water movement to get rid of the weed) and all you do is scrub it off. If I were starting from scratch I'd give the whole hull a couple of coats of Gelshield, then a couple of coats of a hard antifoul compatible with optima, then put optima on top afterwards.
A 2.5l tin gives enough coats for a year's use for me - it needs to be completely dry before immersion though, as will all coatings, read the tin! I change colour every year so I can see where it's worn off. This is a pic of mine when it came out in summer last year - you can see mullet feeding scrapes on the transom, and how the underside of the hull is weed free compared to the waterline 'beard'.