I'm gonna go with my countryman Mike Arnaoutis here. Almost always lost to anyone half decent, having lost against Ennis, Josesito Lopez, Danny Garcia and Chris Algieri. That said, he did beat a genuine title holder once, that being Juan Polo Perez. Only thing is, Perez got a title at Super Flyweight and then lost it in his 1st defense, while Arnaoutis was an 140 pounder . But to be fair, he did manage to get a genuine draw against Juan Urango, who did get a legitimate IBF title at Junior Welterweight. Not exactly underrated, since he didn't really do anything to be rated. But since I think only a select few here know him, I'd say he counts.
Darnell Boone he dropped Andre Ward, dropped Sergey Kovalev and lost a very close SD, stopped Adonis Stevenson. Never a top contender or considered elite, but the fact he achieved all of the above whilst only being considered a journeyman is impressive.
James Tillis. I can't say that he is the most underrated journeyman of all time. I can't say it's a journeyman at all. I would rather call him a gatekeeper. He was ranked 9th only in 1981 by "Ring magazine". I can't say that he is the most underrated, but the only one I remembered. But everyone has heard of him. It is not clear to me how and why he got the opportunity to fight for the title in 1981, when in 1980 he was not among the top 11 according to "Ring Magazine". It is even less clear to me why with 19 wins he was not in the top 11 (1980), and after another win and loss he was ranked 9th (1981). It can be said that he lost to the whole (almost whole) "lost generation of the 80s"
47-26-5 Freddie Pendleton was a world titlest, so perhaps isn't eligible if the criteria is a career journeyman. He was a journeymen for large parts of his career though and was more than a little decent.
Might be reaching, but a welterweight from the late eighties early nineties comes to mind, named Donovan Boucher. He was a scourge for a few top British guys, only coming to grief after respectful kayo losses to Loughran and España.
Some good names already mentioned. Eddie Blunt also known as “ the spoiler “ was a guy who caused some upsets and was not an easy guy to beat. Ross purity has been labeled by a lot of people as a “ bum “ but I couldn’t disagree more. Sanderline Williams was a very tough and durable middleweight who fought James Toney to a draw.
Pendleton was a fighter who I saw many times. Never an easy guy to beat and from time to time upset some good men. I’m sure a lot of guys dreaded fighting him because it was usually going to be a long and dangerous evening
Yeah it's a good name but I don't think it quite fits the criteria of the topic, as Pendleton was a top contender and considered elite for quite a number of the years.
The indestructible Marion Wilson. Took everyone that was anyone on into his 50's and should of gotten the nod against Ray Mercer.