The Scotland international has been part of a side to have kept six clean sheets in their last nine matches.
"Berra is the best defender in the league, for me, without a doubt," McCarthy told BBC Radio Suffolk.
"He's just outstanding, he's big and powerful and wins it in the air, he's quick, he blocks things and is good at defending corners."
Berra has impressed alongside youngster Adam Webster at the centre of Ipswich's defence this season, and McCarthy has previously said Webster will go onto play in the Premier League.
The pair played on Tuesday against Burton as Town ended a winless run of five matches and McCarthy's side travel to leaders Newcastle United on Saturday.
Former Republic of Ireland boss McCarthy said he was impressed by the signings the Magpies made following their relegation to the Championship, such as Matt Ritchie from Bournemouth and Dwight Gayle from Crystal Palace.
"They went out and got players who know the Championship, don't mind playing in the Championship, all want to be out of the Championship again and probably think they can be.
"How they dealt with it, they were good signings in the summer."

No such law exists, but Rishiraj Singh, the excise commissioner in the southern Indian state of Kerala, said such a stare could get a man jailed.
People online asked what might happen if a man blinked, and some quipped that sales of sunglasses would go up.
But some users said Mr Singh had raised a valid point about women's safety.
"A case can be filed against men who stare at women for more than 14 seconds," Mr Singh said in Kochi on Saturday.
The video of his statement has gone viral in the state, sparking humorous reactions and memes.
Some social media users have used dialogues from popular films in Malayalam, the language spoken in the state, to create memes.
Most users have posted memes on popular comedy Facebook pages like Troll Malayalam and ICU.
This meme implies that a teacher must shut his eyes every 13 seconds to avoid arrest.
"Just informed a girl that I didn't like her after meeting her for marriage. She threatened to file a case for staring at her for 14 seconds."
"Bro, what is your crime, stabbing or theft?". "Just went to see a girl for marriage, got convicted for looking at her for 14 seconds."
This meme shows how to time your gaze.
This meme, titled "poor lover", shows how you should interact with your girlfriend to avoid arrest.
Some social media users, however, have supported Mr Singh for raising an important issue of women's safety.
Reporting by BBC Monitoring's Zainul Abid

Derbyshire Police said the taxi driver might have "crucial" information.
A 17-year-old girl from Evesham has been charged with an attempted kidnap of a child in Normanton on 21 September.
Police say the driver may have picked up two teenage girls in Derby on the day of the attempted kidnap.
The two girls are both described as white and age 17.
One girl had shoulder length blonde or brown hair and was wearing a dark blue blouse, a long cream coat, black trousers and black high-heeled shoes.
The second girl had long blonde or brown hair and is believed to be about seven months pregnant.
The taxi driver or anyone else with information about the case is asked to contact police.

PC Gavin Smith, who appeared on Channel 5's Police Interceptors, died from cancer aged 34 on 15 February.
Mr Smith, who lived in Bishop Auckland with his wife Kezi and daughter Tilly, four, joined Durham Police in 2004.
Officers formed a guard of honour to accompany his cortege from Durham Market Square to the cathedral.
Insp Ed Turner of the roads policing unit said: "Gav was one of those characters who just put everybody at ease, no matter who was in his company.
"The station was always a more lively place when he was there. He had one of those infectious personalities.
"He would always put others before himself and right to the end he was focused on ensuring that Kezi and Tilly were OK and they would be provided for.
"In Gav we have not only lost a dedicated police officer, but a true friend."
He died at home surrounded by his family.
At the time, his widow Kezi said: "It has been a real comfort to both me and Tilly that he was so well regarded by so many.
"We will both miss him so very much."
Ipswich Town's Christophe Berra is the best defender in the Championship, according to his manager Mick McCarthy.
[NEXT_CONCEPT]
Social media users have reacted with amused bewilderment after an official said it was illegal for a man to stare at a woman for more than 14 seconds.
[NEXT_CONCEPT]
Detectives investigating the alleged attempted kidnap of a baby are appealing for a taxi driver to contact them.
[NEXT_CONCEPT]
The funeral of a police officer who appeared in a TV documentary series has been held at Durham Cathedral.