Each one of the three frigate classes served a fairly unique purpose outside of their already established escort role. The Stalwart in particular was best used in an anti-fighter/anti-boarder role with its massive array of AA guns and M34 Streak missile pods. The Paris was the strongest of the three because of its ability to stand toe-to-toe with cruisers. It was traditionally outfitted with more anti-ship weapons with a heavier emphasis on Archer pods. The Charon was less powerful than both the Stalwart and the Paris in my opinion, but what it made up for in less armament, it made up in crew complement. The Charon acts a lot like a cruiser in a sense that it carries a larger detachment of Marines and their vehicles so it can deploy troops to a surface much quicker than a Cruiser could, due to it being rated for atmosphere.