Best defensive pressure fighters ?

I think of Loma when I hear this. The dude was all up in a fighters face for all the rds and despite being there and pouring on the offense, he was incredibly difficult to hit in return.

Canelo deserves some credit here. When he's pressuring you, he keeps a very tight and versatile defense many times. There are some times he gets overly reliant on a high guard, but his defense is still good.

The only answer here is Roberto Duran.

Golovkin was quite defensively responsible for a guy who constantly came forward and had an iron chin to fall back on in case he did get hit

Past would be Duran and Chavez for sure. Roman Gonzalez at his best was great. Beterbiev currently.

In-fighters with great defense would be Jake LaMotta, Dwight Muhammad Qawi, Henry Armstrong, Julio Cesar Chavez Sr, Roberto Duran, and Mike Tyson. From the present, Isaac Cruz and Christian Mbilli being the best examples of a in-fighter with actual but basic defensive fundamentals. Roman Gonzalez is a pretty great example as a modern fighter. If you mean fighters that also apply pressure at midrange, they are bit rarer to find. At least from what I seen so far, I could be wrong. There is Joe Frazier, Evander Holyfield, Gennady Golovkin, Vasiliy Lomachenko, and Artur Beterbiev have pretty good defense. In my opinion, Errol Spence Jr's defense mostly relies on him managing his distance and blocking due to his size advantage at Welterweight, he can be caught in between shots. He at least has an impressive work rate that works well with his long reach. Manny Pacquiao is hittable, but he tends to slip punches with his reflexes and outwork or catch off guard his opponents with rapid combinations. When solely focuses on defense he seems pretty good though. He also had a good chin to compensate.