Best TT specialist ever?

Depends really whether you mean best TT rider in general or rider who excelled at TT but did not do much else.

Guys like Anquetil and Indurain won five Tours while their best asset was time trialing. Then Boardman is a better example in the latter category since his biggest successes were in ITTs, mainly with WC title and several yellow jerseys as a TdF prologue winner.
May 14, 2019
I mean best TT rider in general, I'm disregarding whether they excelled in other disciplines, for example a good way of putting it is if everyone in their prime raced eachother in a TT who would win?
I mean best TT rider in general, I'm disregarding whether they excelled in other disciplines, for example a good way of putting it is if everyone in their prime raced eachother in a TT who would win?
My vote would go to Indurain. The way he dominated was insane and no one put out more power.
For what its worth, Cancellara has had the largest (2006) and second largest (2009) gap in ITT world championships. But of course, thats only a limited view. Merckx, Indurain, Armstrong, Martin and Cancellara had periods were they were unbeatable. Also Wiggins in 2012... ;-)
Unfortunately, "for what it's worth" isn't a great deal because it only deals with the mid-90s onwards. And using the Worlds as the primary guide, strictly speaking while Martin and Cancellara are rightfully the top 2 for the modern era (arguably Armstrong belongs in there too), Rogers is the next most successful ahead of Ullrich. 2012 Wiggins was practically unbeatable, but the fact that he didn't have the consistency of Cancellara or Martin (he goes from being a prologue specialist who is pretty good in mid-length TTs to a long-form TTer quite late, and then his era of dominance is brutal but brief).

Prior to that generation, the GP des Nations is perhaps a better guide, being a semi-classic in its own right and an informal World Championships in the days when there were none. Jacques Anquetil won it on nine occasions, more than anybody else, and the next most successful rider is Bernard Hinault with five wins. However, that is also fraught with some issues as it ran late in the season and often that impacted the field, with riders preferring to build up to Paris-Tours or the Italian autumn classics. It waned in importance in the 80s and it is notable that Indurain never won it during his reign of terror.

If we include Grand Tours, then Merckx obviously comes into the discussion once more, as does Indurain, as his victories were built around ITTs which stomped the field by colossal margins.

Another event that would have to be considered in the grand scheme of TTing is the Hour Record. Anquetil improved the hour record on two occasions, the first time taking the record of Fausto Coppi, who is another worth mentioning. However, neither of Anquetil's records lasted long, being outmeasured by Roger Rivière and Ferdinand Bracke after only a few months respectively. Merckx's 1972 record, on the other hand, has stood the test of time as perhaps the most important of all Hour Records, standing for twelve years and serving as the dividing point between the outright, only partially restricted world hour record, with all of the technological advances of the ages, under "best human effort", and the more restrictive "UCI hour record" which limited riders to equipment similar to that used in Merckx's time. Indurain has a "best human effort" and a number of others have two. Francesco Moser is a worthwhile name to drop, as is Chris Boardman, who is the only man to hold records within both the "best human effort" and the "UCI hour" categories once these had been separated post-Merckx. Tony Rominger is the man who made the biggest advancements of the distance, and also won the GP des Nations twice, but I find it difficult to suggest him on the basis that, for the most part, he got fairly comprehensively beaten in the GT time trials of the time by Indurain (Boardman is also impacted by this). Graeme Obree is the other rider with two records in the "best human effort"; I find him a bit of an outlier and a difficult one to rate. He was not especially successful on the road, but a lot of that was to do with the lifestyle and habits of the péloton of the time and also his own personal characteristics and issues. However, his importance to cycling history is in his innovation and I would consider him more of a maverick and an important innovator than an in-his-own-right bona-fide great.
Out of the riders I've seen then Indurain and Hinault. I thought Spartacus was stronger than Martin when TTs were his sole focus. After he really started focusing on classics then Martin gets the edge.

Never saw Merckx or Anquetil so I can't really comment their wins.
IMHO there shouldn't be any doubt about Anquetil, Coppi did similar showings during his career but not so many times and starting already at 19 like him. If I have to make a podium probably I'll round it up with Indurain that is the strongest I've seen with my eyes.
Has to be Big Mig for me. Simply humiliated the rest with his margins of victory in TdF time trials and while I found him a bit boring to watch he was undeniably hugely impressive.

Hard for me to rank anyone whose peak was earlier than about 1993 as I didn’t see them perform and it was a far less specialised era.

Of the last 20 years then Cancellara stands out for me for his long reign as a winner in this discipline.