Sure, I'll put forward some opinions. First, I disagree strongly with there being an S+ rank as we have currently. While S implies a pokemon is one of the best in the meta, which is absolutely true of Tyranitar, S+ implies that it shouldn't be dropped from any team. This isn't true of Tyranitar, because while it is the best and has a lot to offer every team, it doesn't offer so much that dropping it will always make a team worse.
My rankings for S to the A- are as follows:
S Rank: Tyranitar, Gengar
A+ Rank: Skarmory, Suicune, Blissey, Jirachi, Metagross, Swampert, Celebi, Salamence
A Rank: Zapdos, Dugtrio, Aerodactyl, Snorlax
A- Rank: Magneton, Starmie, Flygon, Heracross, Jolteon
Gengar is one of the most offensively threatening pokemon in the tier. It offers powerful status in either Wisp, or Hypnosis, and also has amazing coverage that can hit a huge portion of the tier. Blissey risks being exploded on, and even without explosion, with a combination of taunt and wisp, supported by sand and spikes, Gengar can wear down Blissey over the course of a game. As for recent development, this year we've seen bulky Gengar get more and more popular. This lets it live Tyranitar's pursuit trap, and generally gives it more longevity. For these reasons I believe it should be the only other pokemon in S rank, and I'll now explain why I don't think any pokemon other than TTar or Gengar deserves to be.
Celebi should certainly drop from S rank. Defensive sets let Skarm and Forre come in easily, and lay down spikes, while it can't really do that much in return. This is a very notable disadvantage. Depending on what moves it chooses to drop, it can find itself in serious trouble.
If it doesn't run Hidden Power Grass, it's unable to kill Dugtrio in 1 hit, which leaves it much more vulnerable to trapping. It is also unable to damage Tyranitar outside of Leech Seed. However, without Psychic, Celebi can't take on Taunt Gengar well at all, and also lets Heracross come in. If you choose to run both, then you miss out on the many useful support moves that bulky Celebi can run, such as Perish Song, Screens, BP to keep momentum. Celebi also has CM sets, and can BP those boosts to team mates. However, I don't believe these other sets are strong enough to keep it in S either. They can also be roared out by Zap, or whirled out by Skarm, though they do get a decent hit off before that happens. Celebi has many merits as a pokemon, but the drawbacks are enough to keep it in A+.
As for Suicune, I don't believe this deserves S rank either, although it is a closer case. When you look at Suicune, you have to weigh it up vs other bulky waters to see how good it is. Suicune is the best water type in the tier, but not to such an extent that it deserves S. Compared to Swampert, it lacks a rock resist, which is pretty crucial. Secondly, it also takes sand damage whereas Swampert does not. Therefore, Swampert can run protect to gain additional recovery, Suicune can't. As a result, Suicune runs rest. This gives the opponent free turns, and makes Suicune not as strong of an answer for pokemon such as DDttar and Aerodactyl. Due to the lack of ground typing, and therefore not running protect, Suicune becomes a much easier target for pokemon such as Metagross to boom on. Those defensive merits Swampert has means it tends to get higher usage than Suicune. However, overall, Suicune is still the best water type. It offers a strong wincon with its CM sets, and while Swampert gets destroyed by surprise HP grass from pokemon such as a TTar, Suicune can shoulder them quite easily. Suicune also can very strong with offensive sub CM sets, which are fantastic considering how Fire Blast Blissey has become more common. However, it must give up bulk, and heavily dislikes sand and spikes. I don't think it is strong enough for S.
Finally, the last candidate is Skarmory. I don't think that deserves S. Skarmory is integral to a lot of teams. It is unquestionably the best spiker in the tier, it offers strong defensive merits, isn't set up bait because it whirls, and can wear down most pokemon it is afraid of, such as offensive Zapdos, Moltres, Jolteon etc with toxic, while it recovers by using Protect. However, it too has enough disadvantages to keep it out of S rank. The only way it has of applying pressure is through Spikes, and Toxic + Protect stalling, so in matchups where the opponent has a hazard remover that doesn't care about toxic, such as Refresh Claydol, Skarmory will be less useful. However, that's a lesser point.
While Skarmory sets up spikes, the opponent has a free switch into Gengar, one of the most dangerous pokemon in the tier, which can be very punishing to switch into. In addition, I don't think a pokemon being trappable is such a huge disadvantage. However, the difference is that TTar, Celebi, can KO Dug if it tries to come in and trap them. Skarmory can't do anything against Magneton short of a very very niche offensive HP Ground set. Skarmory is exceptionally susceptible to trapping and I think that is the key difference. The fact that spikes have decent counterplay, and in particular that Skarmory can be punished so heavily by Gengar and Magneton, are the reasons why I think it should stay out of S.