In my opinion, Moltres is without a doubt the best Pokemon in RU. It 2HKOes nearly the entire metagame with Fire Blast and Hurricane alone, and not even Slowking is a counter anymore. It has a bunch of viable sets, from Life Orb to Choice Specs to SubRoost to SunnyBeamer. Almost anything slower than it is destroyed, and it has pretty good bulk for an offensive Pokemon too, meaning that Volt Switches from the likes of Scarf Rotom-C, Scarf Manectric, and Rotom don't KO it. Like I said before, it's easily the best Pokemon in the tier.
Its only two common counters are Lanturn and Munchlax, of which only the former is frequently used by the top players. However, Moltres has a huge number of checks, the best one being Stealth Rock. Losing half of your health to Stealth Rock alone is extremely crippling, even if Moltres is immune to all other entry hazards. Roost is good for healing the damage off, but if you can force Moltres out before it has a chance to heal, it's pretty much dead as long as you keep your hazards up (and in this metagame it's almost necessary to have a spinblocker). Moltres struggles against offensive teams though, since a lot if things carry a Rock-type attack. Almost all of the tier's Fighting-types use Stone Edge such as Unburden Hitmonlee, Primeape, and some Gallade. Entei also forces it out pretty nicely, since I don't think Life Orb Hurricane KOes without Stealth Rock, while even when Roosting Stone Edge does 80%. Accelgor, Sceptile, and Typhlosion all commonly carry Hidden Power Rock, and there are many Electric-types in the metagame that outspeed and KO Moltres, with or without a Scarf. Manectric is capable of KOing Moltres with an unboosted Thunderbolt, as is Rotom-C. Rotom naturally outspeeds Moltres, and is guaranteed an OHKO with Life Orb Thunderbolt, and Galvantula can use Thunder to dispose of Moltres. There are viable Aqua Jet users in the metagame as well, with Kabutops resisting both of Moltres's STAB moves, and Feraligatr having the bulk to take a Life Orb Hurricane. Although not a hard counter anymore, Slowking is still a strong check to Moltres and it'll probably continue to be on most teams. And while Hurricane gets it some crucial KOs, its god-awful accuracy means that you probably won't hit two or three in a row, and that can be taken advantage of.
The set I've used a lot between RUgged Mountain matches and PS! ladder play is the classic Life Orb set, most certainly Moltres's best set.
Moltres @ Life Orb
Trait: Pressure
EVs: 4 Def / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Fire Blast
- Hurricane
- Hidden Power [Grass]
- Roost
I think we're all pretty familiar with how this set works, but I'll go over it quickly anyway. Fire Blast is still your best STAB move because of its superior coverage and accuracy, and bits most things pretty hard. Hurricane should be used sparingly from my experiences, since you can't really count on it, but it's still really useful to 2HKO Slowking after Stealth Rock and OHKO Gallade. HP Grass hits the same things that it has in the past, such as Kabutops, Rhydon, Omastar, and Lanturn. It's also good for when you can't afford a miss. Roost is the key to the set though, and using it at the right time often makes the difference between a sweep and dying. Moltres can destroy almost everything with the appropriate move, but it can be played around. A lot of the time there's no need to predict when using it, since you can use Hurricane when you're in against Tangrowth and never pay for it even if they switch to Slowking since you 2HKO that too. It hardly ever sweeps though, because everyone carries a Moltres check. I typically only get a kill or two per game, but games have been decided on Moltres Speed ties.
Honestly, I'm not completely decided on Moltres, but as of now I wouldn't choose to ban it. Right now there's nothing that makes me think it should be banned, so by default I think it shouldn't be banned. Feel free to try and change my mind though.