I think Gretel was given a bit of "free reign" on what she said ... with only a few prompts from the control people via earplug. But I get the impression that Sonia, on the other hand, appears to be told everything that she should say via the earplug (ie, the show is now very "scripted"). It's like the show is making an effort to avoid any controversies (which have plagued previous Big Brothers). Perhaps I am wrong, but that is how it all looks to me. Sadly, this effort seems obvious and is not invisible.
If I am correct in my assumption that the show is way more "scripted" now, via the earplug, then it makes it difficult to compare Gretel over Sonia. If Sonia wasn't "scripted", then it would be easier to do the comparison.
If I am wrong about it being "scripted", then that's my comparison right there ... Sonia appears to come across as being "scripted", but Gretel was more spontaneous and able to ad-lib (making Gretel better than Sonia).
But, give Sonia a chance ... it's only day 3. Gretel got confidence from the benefit of time and doing many shows. I'm sure Gretel was a bit "rigid" in the first few shows too. Sonia's had only three days. Sonia is still finding her feet.