600W is going to be a challenge in supplying an average 300Ah/day. That will require ~1000W.
For solar panels, I just shop by price and size for the area I can fit. Size is a tough one, as most of them seem standardized for any given output, and this standard size changes over time.
We have had expensive top-of-the-line panels, as well as the cheapest no-name panels, and have not seen any difference among them when compared W to W. The differences tend to be in the efficiencies of the cells used, which manifests itself in the panel dimensions, or more wattage per fixed dimension.
That is for fixed rigid panels. I've yet to see a flexible panel that produced anywhere near specs in real use, or lasted more than a couple of years. If you can fit rigid panels, you will spend a lot less money, and have a lot more power, for the life of your boat than if you use flexible panels.
Mark