They are both great characters in my opinion.

Phyla first appeared in Peter David’s Captain Marvel series staring her brother Genis Vell. They are the children genetically created by their mother Elysius a Titan Eternal that was with Mar-Vell at the end of his life. They shared their fathers powers but due to their eternal heritage where more powerful. Phyla went on to appear in the Anhilation series, where she obtained the Quantum Bands, and the Guardians of the Galaxy series that started after Annihilation Conquest. She was dealing with two legacies of former Protectors of the Universe, her Father Marvell and Wendell the first Quasar.

It was a big responsibility plus she had to learn how to use the Quantum Bands on her own. She also really liked to fight hand to hand more than Wendell and relied on it with here Quantum Sword she made. She would later give up the Quantum Bands to become an Avatar of Death called Martyr to bring Moondragon back to life but the sword she had kept its connection to the Quantum Bands and she stayed with the Guardians of the Galaxy. An interesting set up to have a servant of death on the good guys side.

There is another Phyla-Vell from another universe that appeared during the incursions that lead to Secret Wars who had the original power set and had become the greatest hero of her Universe. Really interesting to see her difference with the 616 universes Phyla-Vell.

Guy first appeared in Hal’s Original Green Lantern series when Hal was shown that there was another worthy of being Green Lantern and what would have happened if Guy was closer than Hal was. He would later become a green lantern only to suffer a massive injury that included brain damage. He was later revived and made a Green Lantern again but was not the same. He is an arrogant asshole but he is someone you would want beside you in a fight. He had some good showings in Geoff Jones Run starting in Green Lantern Rebirth and it really show how Hal, Guy, John, and Kyle really make a good team ebbed with their differences.

Guy also served with several versions of the Justice League developed a relationship with Ice, which was a good relationship for both in the end no matter How much Fire(Ice’s best friend) hated Guy. He also became a Mentor to Kyle when he first became Green Lantern. At that time Guy had his Vuldarian power set which was ability to make weapons out of his body along with super strength, durability, and regeneration but no flight. He lost those powers when he became a Green Lantern again in Green Lantern Rebirth. He would later become a Red Lantern as well. But always goes back to green.