So in the professional industry, 2 part paints are used which do have a harder finish and generally last longer. This is what is usually sprayed on the huge yachts and mostly on boats during a full restoration. They cost more and are harder to apply.
I have used the Interlux on my bow pulpit and swim platform and the gloss and hardness is amazing. They usually hold up many many years without even applying wax. Thus why used on the big boats.
However, they are harder to repair as they don't allow blending like the one parts usually do.
The one part paints of today though are pretty amazing and hold up very well. Andy on Boatworks has been impressed with the Alexseal brand and it seems very easy to apply, is very forgiving to repair, sand, polish, etc.
I have re-gelcoated my entire bottom hull, all hatches and pulpit prior to last paint as mentioned above on the pulpit. So far, the Interlux is truely amazing with it's high gloss and easy to clean. Much better than the gelcoat which is porous and has to be really taken care of more than the paint.
Guys, there are plus and minus for all 3 applications depending on what you are doing.
I also wanted to repaint the top of my hardtop. If I was to do that, I would likely choose the Interlux again, but it is hard to apply. I would use the texture they recommended with their paint. I forget what it was, but it was excellent. On the hardtop, if you need to get up there and fix anything or install anything, if no texture, it can be very dangerous and slick since it slopes in all directions. Also, just crawling around up there will scratch and mar the surface. In my approach, I would put some texture.
Underside is great to make a color so it can reduce some of the glare, but think top is best with original. The reason I used Interlux in the first place is the color is so close of a match to the Grady color, it is hardly noticeable next to the gelcoat.
I have sprayed Imron (Urethane), Sherwin Williams Sunfire (2 part Acrylic Urethane) and many acrylic enamels and epoxies in the years past any the one that holds up the best over time has always been the 2 part Acrylic Urethane paints. Those were used for automotive and industrial industry. For marine, my experience is only with the Interlux so far. But I was intrigued by the Alexseal that Andy has demostrated many times in his videos.