Depends on the years; really does.
The Pro, Semi Pro, and Pro Tour always throw me off, so I stay out of that part of it.
I'll just stick with the top few, the years I know more about. There's always some debate.
I've not had any models other than those listed here, and have not owned a "straight" Carbon or an Elite RS.
There were many lower level models, which were also, generally, better equipped than the price point competitors.
Not always, but generally. There was a Lemans mixte in there, too, and a track bike, the Trac.

Bear in mind I am by no means an authority or an expert on this;
I've just had some and am perfectly willing to say what I think, and claim the right to be wrong.
(Sort of the opposite of being married)

1983:
Turbo
Lemans RS

1984:
Turbo
Comp TA
Lemans RS

1985:
Cinelli Centurion Equipe vs. Prestige for top of the heap.
Dave Scott Ironman
Elite/RS vs. Lemans/RS (depending on whether you liked Shimano or Suntour)

1986:
Dave Scott Ironman
Elite/RS vs. Facet (steel w/Shimano 600 vs. aluminum w/Suntour Sprint)
Lemans/RS (I've not seen an '86 that I was sure was an '86, but LBS says they were out there)

1987:
Dave Scott Ironman Master (600EX)
Dave Scott Ironman Expert (105) some like that 105 better than that 600EX
Lemans/RS

1988:
Dave Scott Ironman Carbon (Dura Ace)
Dave ScottIronman Master (steel 600 tricolor) vs. "straight" Carbon (CF 600 tricolor)
Dave ScottIronman Expert (105)
Lemans/RS (Taiwan)

1989:
Prestige (Dura Ace) I've only seen one. A BF member has a blue/white fade.
Dave ScottIronman Master (600 tricolor)
Dave ScottIronman Expert (Suntour GPX)
Lemans/RS (Taiwan)


The wild card is sort of that later 80's Prestige; I think it was '89, but the decals are more in line with the 88's.
By '89, they'd subdued the decals a bit. In '88, they were "busy," to say the least.

I'd also like to stress that there was very little difference between the Ironman Expert and the Ironman Master, until 1989.

Anecdotal stuff:
The Turbo, early Prestige, and Cinelli-made Equipe are often said to be fully chromed under the paint. I know of a Turbo that was stripped 100% and if the frame isn't polished, it sure is some smooth "rough" work. The Prestige is chromed, but not polished chrome, under the painted parts. My paint guy says the Equipe is chromed and "good enough to leave stripped" all over, but the only thing I know for pretty much certain is that the forks on all three of those models are polished chrome plated under the paint.

The Elite had the same components one year as the Ironman, at least one of them I saw did.

The Facet was raced by the all-female team, and their bikes were pink. Later, they raced re-badged Italian bikes.
Rebecca Twigg was a team member. It was Centurion's only offering, that I know of, in aluminum. Some think the Facet was the equal of the Ironman in 1986, due to the racing team. Having both, I sure can't choose based on frame, components, or wheelsets.

Of those who've had several Ironman bikes, some feel the '86 in red/white with the copper Araya's and red-hooded DC brakeset was the smoothest and most elegant of the Ironmen. I can't really argue with that.

In 1989, Centurion stated they'd tweaked the geometry on the Ironman. Those who have had several, including the black '89 Expert, seem to all report that the black Expert frame is a bit snappier than the other Ironman models. That is also my experience. The Master and fade Expert models seem to be smoother than the black Expert model in '89.

All the late Ironman bikes had tires that were generally hated, Panaracer Technova II's. They said 700x19 on the raised lettering, and 700x18 on the labels. They were hard as rock, and this contributed to lots of truing needed on the later model Araya CTL-370 rims if the bikes were raced hard.

Scarcity is an issue that doesn't always make the price go up, for Centurions, anyway. The Ironman can't be that rare, as I have not once gone on a group ride or a century when someone didn't recognize the bike and say they once had one, much like a Puegeot or an older Schwinn.

My rarity ranking:
"straight" Carbon model
Prestige
Facet
'87 Master, Turbo, '85 Ironman
Comp TA, Elite RS, '86 Ironman
Cinelli Centurion Equipe-most are in the hands of one dealer.
'88 Expert, '89 Master
'89 Expert
'87 Expert, probably the most numerous.

Pricing, an educated guess:
Cinelli Centurion Equipe
Turbo, Prestige
Facet
Ironman models
Elite RS
Lemans RS
Elite
Lemans