Both players arrived in the summer to boost Sunderland as they prepared for this season's return to the Premier League.
Former Arsenal captain Xhaka has been outstanding from day one for the Black Cats, while striker Brobbey has come into his own since the New Year.
Asked if Xhaka should be regarded as the signing of the season Goodman, speaking exclusively to Tribalfootball thanks to the home of Liverpool away match access online said: "I'm struggling to think of a signing that has had a single bigger impact than he has had on that team.
"I'm talking about the single biggest influence on a team. And I don't see... I'm even trying to think about who Bournemouth brought in because they're normally very, very good. The Newcastle ones haven't worked out. I mean, you could argue, particularly for a golden period of a couple of months that Calvert-Lewin had a real impact at Leeds.
"Again, over the course of the full season, no. Honestly, I'm looking through. No, I can't have it that any new signing has had a bigger impact on a team's performance than him as an individual. No, I can't have it."
Meanwhile, asked if he's been impressed Brobbey this term and if the Dutchman can get even better next season, Goodman was adamant.
He said: "Yes and yes. I like what he brings to the table. I love his physicality. He's almost a throwback, in that he's almost saying to centre-halves, if you want to fight me, let's fight. It's almost a sort of a throwback to the old days and they can't live with his power and his physicality.
"So, the best advice to central defenders is don't fight him, don't wrestle him because you're going to be onto a losing battle. I don't think that there's a no. 9 in the Premier League that holds the ball up as well as him. And that allows, what you've got to appreciate is that Sunderland are a team that in most games, they have a lot less of the ball than the opponent.
"Their average possession in the Premier League, there's only four teams that have had less possession. It's 43.9% they average. So my point is, when you're a team that can't really control games through dominating the ball, you need your centre-forward to be able to hold it up and hold on to it. And he's been priceless in that regard.
"I know he's only scored, I think it's six goals, and people will look at that and go, why are you bigging up a striker that's only scored six goals? He just brings so much more to the table. The Sunderland players know they can roll the ball into his feet and he can protect it and hold it and wait for support to arrive.
"I think next season he'll score more goals, if I'm honest. He's still had to learn about what the Premier League is, how it rolls and I think he'll score more goals next season.
"He brings so much more to the table, and for what they paid for him, I think he's been a bargain."