I never understand the assumption that "tweenies" basically decide who wins in the final. I think it's just down to the casual audience, who are much more likely to vote in the final than earlier in the series. Anyway...
Mark - Sorry, I don't think he stands a chance of winning. Frankie and Jake both received more votes than him on Saturday, and he is trailing behind at the moment. I think he'll be out this week.
Simon - I still don't think he can win. For someone to be so unpopular to be in the dance off in week three and week five (despite being a good dancer), it would take a miracle to turn that all around. I can see him leaving in the semi final, or being 4th in the final.
Pixie - I have no idea about Pixie to be honest. She could be storming in the votes, or she could quite literally be at the bottom. She's a good enough dancer to be in the final (and I'd be surprised if she wasn't there), but she could end up like another DVO/Natalie Gumede. If I was to place a bet, I'd say she'll be a runner up in the final.
Caroline - She's had her "wow" dance now, which has put her back in the competition. I'd be surprised if her increase in momentum hasn't translated into more votes. I think she could avoid the dance off for the rest of the series and reach the final. She stands a good chance of winning.
Frankie - Frankie clearly has some kind of fanbase, and I think she would appeal to casual viewers over, perhaps, Pixie. She's not the best dancer, but she has a lot of things going for her. I think Frankie is probably the most likely winner at the moment.
Jake - Had I been asked in week five (or even last week), I'd say Jake would win. But he seems to be going down the Susanna-route, of slipping behind with the judges at the final hurdle. I wouldn't be shocked if he was bottom of the leaderboard this week. I think he'll avoid the DO this week, but I'm not sure about the semis. If he gets to the final and re-does some of his best dances, he stands a very good chance, but at the moment, I'm not sure.
To sum up, I think, from highest chance of winning to smallest chance: Frankie > Caroline > Jake > Pixie > Simon > Mark.