Witsel, 29, has been in superb form since linking up with the Bundesliga leaders following an 18-month spell in China.
The Belgium international has won league titles with Standard Liege and Zenit St. Petersburg in the past – as well as playing for Portuguese giants Benfica – but he says that Dortmund is the most impressive club team he has been part of.
“In my career, yeah, because it’s the first time, for me, I’m in the top level,” he told bundesliga.com.
“I don’t mean only BVB but also the Bundesliga. So I think, yeah, with the Belgium team and Dortmund - it’s the best one.”
Watch: Check out Witsel's Goal of the Month winner from August
Witsel arrived at Dortmund after a glorious summer with Belgium, who finished third at this year’s FIFA World Cup after falling narrowly to eventual champions France in the semi-finals.
Any suggestion that the Liege native might suffer a post-World Cup hangover was quickly dispelled. He came off the bench to rescue Lucien Favre’s side in the DFB Cup on his club debut against Greuther Fürth, before scoring on his Bundesliga bow in a 4-1 win over RB Leipzig.
Earlier this month the classy central midfielder even got his first UEFA Champions League goal for the club when Dortmund maintained their unbeaten start to the season with an eye-catching 4-0 success against Atletico Madrid.
“It was a big challenge to come here, for me, but I knew I had the quality to play here,” he said. “If not I would decide otherwise – stay in China or I don’t know.
“But I’m really happy. I didn’t expect for the team to play like this because we have a lot of really young players and a lot of new players also. Normally this takes more time than what we’re doing now, but it’s good for us.”
Witsel believes Dortmund should be proud with how they “played smart” against Atletico, although he says they plan to impose their style on whoever they come up against.
Favre’s team have been ruthless this season – scoring 29 goals in nine Bundesliga matches – but their new midfielder is not able to put his finger on exactly why they have been so clinical.
“I really don’t know,” he said. “It’s not an accident because if it’s an accident it happens only one time in one game. But you know with our style of play, we have really talented players. Everybody, technically, is really good.
“Sometimes we take a lot of risks – from the goalkeeper also - but that’s our style of play. Like I’ve said before, we will not change it against anyone.”
While Witsel has added muscle and craft in midfield, it also helps to have talented attackers - and Dortmund are not short in that department. Captain Marco Reus has led by example, new signing Paco Alcacer can’t stop scoring, and youngsters Christian Pulisic, Jadon Sancho and Jacob Bruun Larsen have all made key contributions.
“Offensively we are really strong,” Witsel said. “We have players who can make the difference.
“Marco, Christian, Jadon - Jacob also. So, offensively we are doing really good. Even if we are losing one or 2-0, we will give everything to score more than the opponent.“
The other teams in the Bundesliga – and the rest of Europe – have been warned.