The Push The Button duo argued that new panelists David Hasselhoff and Michael McIntyre have put a "spark" back into the contest and been fairer in their assessment of hopefuls.
Donnelly told The People: "The new panel is great. They have that spark BGT had in the first year. That has been lost over different series.
"This year it has been so much fun. Simon just put all the dogs straight through. But Michael, Amanda and David have been giving everyone a real chance and debating each one for ages. It is a lot fresher and much more exciting."
"The two new judges give it a whole different feel. They like new types of acts that the old judges didnt, so everyone has a better chance. Magicians never got much of a look in with Piers and Simon as they did not have much of a sense of humour. But David and Michael do. So the acts stand a better chance, we think."
When pushed for more details on the new arrivals' playful side, McPartlin said of Hasselhoff: "He was great fun. He would run in every time to the Baywatch theme. Then he would talk to KITT through his watch."
The Geordie pair further admitted that they are unsure whether Cowell, who will return for the live shows of this year's series, will be satisfied with the acts that Hasselhoff, McIntyre and their fellow judge Amanda Holden have selected.
"Without him on the show it is wide open to anyone," Donnelly confessed. "Is Simon happy with the lineup? I've no idea. I hope so, but we haven't heard from him since the auditions ended."
Britain's Got Talent will return for a fifth series on April 23.
> Ant and Dec: 'Got Talent feels fresh'