best mon 10/10
That being said, Ho-Oh had modest beginnings, mainly because teambuilding in GSC Ubers is limited and Ho-Oh offered little to the table in comparison to the metagame staples.. Mew/Snorlax/Mewtwo are requirements, Lugia is almost a requirement, and Heal Bell is a requirement (Celebi/Miltank), so that really only gives you one or two teamslots to play with, and the usefulness of spreading burns (what Ho-Oh was known for) could be somewhat limited at times since everything has recovery and most teams have clerics. That being said, Ho-Oh is great at pressuring key staples like Celebi and Steelix, and SD Mew usually could not OHKO it without resorting to Explosion. Though it lacks good physical STAB, it makes a decent Curse user with Sacred Fire to ward off potential checks such as Steelix, TTar, and Skarmory. It can also run an all-out attacking moveset with EQ/Shadow Ball/Thunderbolt as possible coverage moves, but its lack of physical STAB hurts it vs Snorlax and the odd Blissey.
In ADV, things started looking up - Ho-Oh got a nice friend in Groudon, who could provide sun for it to abuse Sacred Fire and a very fat resistance to Rock Slide. Choice Band and the EV limit also improved Ho-Oh's offense considerably, and it was now able to deal effectively with special tanks such as Latis and Blissey using a physical set. However, it still lacked good physical STAB, wasn't much of a sweeper, and had very annoying weaknesses to Rock Slide, Thunder, and Surf, which can make it somewhat hard to utilize. It was a definitely a threat and it found good use on some teams, but it wasn't dominant. Not yet, anyway.
DPP was when Ho-Oh really started gaining prominence, though it had a bit of a rocky start. It finally gained physical Sacred Fire, but DPP Ubers was quickly dominated by rain based teams as Kyogre gained massive benefits from Choice Specs/Scarf and further cemented its #1 spot in the usage statistics. Ho-Oh still only had unSTAB Earthquake with which to fight back. It also lost physical Shadow Ball and did not gain a comparable replacement, giving it issues against Latis and then newcomer Giratina-O. Stealth Rock was also a huge downer, as Ho-Oh was not overly fast and losing half of its health just by coming in ruined its solid bulk. Spinning was also somewhat difficult as Giratina(-O) were extremely difficult to kill and Forretress, the only real viable spinner, had massive trouble dealing with them. Between Stealth Rock and troubles dealing with the heavily Fire resistant metagame, Ho-Oh struggled a bit to find significant usage.
However, HGSS finally gave Ho-Oh good physical Flying STAB in Brave Bird, and that changed everything. It could now effectively fight the Latis again, Kyogre went from being a good counter to a shaky check at best, Giratina-O struggled to switch-in - the phoenix went from having several solid switch-ins to almost none as very few Pokemon could withstand the high-power physical STAB attacks Ho-Oh had always needed. It found easy switch-ins on most teams due to the pressing need for Steels to combat Dragons, and was tough to KO assuming you could keep Stealth Rock off the field. As in DPP, its most common set was SubRoost, and it was usually guaranteed to get a kill if it managed to get in on your Steel. Though Stealth Rock was still a huge issue, the reward for using Ho-Oh was now much greater, and that helped give it a spot on many sun offense/stall teams as a bulky, nuclear attacker that could check things like Darkrai and Latis.
Ho-Oh got even better in BW2. Though it introduced more things that Ho-Oh could check (CM Arceus formes, Ferrothorn, Genesect), and gave more viable spinners (Excadrill, buffed Cloyster, Kabutops was starting to pick up), the biggest buff Ho-Oh got by far was Regenerator, which gave it a little defense against Stealth Rock and massive tanking ability once the hazard was cleared. It also made Choice Band quite viable again as it no longer needed Roost to try and stay alive against Sneaky Pebbles, giving it even more damage potential. Ho-Oh ended up becoming the face of BW sun offense and also found considerable usage on sand and stall teams. Most sets were LO Roost or Choice Band, though stall teams also started making use of physically defensive sets that could check a wide range of threats such as Darkrai, EKiller, Psystrike Mewtwo, and Lati@s.
Overall, Ho-Oh started off as a somewhat mediocre wildcard and finished as one of the most dangerous Pokemon in the entire game as it was slowly buffed with each new generation. Many people have gone so far as to say that Stealth Rock is the only thing keeping the phoenix in line nowadays. Even in the earlier gens, don't underestimate this bird. Or birds in general, really.
tl;dr kacaw