I wouldnt axe any of them tbh. I dont see a long term future for Sylvie on the show but I have a feeling she is only temporary anyway. I think Babe might have a limited lifespan as well now that all her evil deeds are coming to light. Tina is the weakest and least developed of the other Carters imo, I do like her at times and think she was good in the storyline with Tosh but the pairing with Sonia and lack of her own storylines has done her no favors.
I think Lee gets a lot of hate on here but I actually really like him and I think he was good in the depression storyline, im not keen on Lee and Whitney together though. Johnny 2.0 hasnt impressed me massively but he has not been back long and has not really had a major storyline except convincing Ben to report the attack to the police so I would like to see more from him before I make up my mind (Johven anyone?

)
Shirley has been on it for years now and Mick and Linda seem generally popular so I doubt they will be on the axing table.