Chris top weeks 1-7. Winning the wildcard would have enabled him to win week 1 as it helped Amelia Lily in her return in series 8.
About 70% of the voters in the early live shows are 40+ year old females who would empathise with Chris. The obvious bullying also helped him gain momentum as the underdog with several campaigns to get him through each week as the anti-XF act. (This of course is stupid because the show continually pointed out their own nasty behaviour toward him to create the scenario where people vote for him to bring in revenue for Syco).
I think James won week 8 and 9 after being in the bottom 2. Tulisa's little rant telling the public to "vote for the right contestant, not for who who like" was a stroke of genius, with The Sun & The Mirror both giving James major coverage and starting "James to win" campaigns.
Jahmene has been over-pimped by the show. Even excusing the over-use of sob stories, the constant religious references have been hilarious. The "stairway to heaven" staging, sing "Angels", Nicole calling him "blessed" etc have been a massive contrast to the demonic head with laser eyes treatment Chris received.
So I think Chris, topped for most weeks, then fell away as the show said "vote for him if you're an 82 year-old woman who knows his nan."
James was middle of the votes most weeks but wasn't gaining until the XF "James to win" campaign started.
Jahmene was close to the top in the early weeks but never gained many new votes as the show went on and was close to going out at one point, which is why the show started on the heavy pimping.
Also, there have been rumours that Ella was close to the bottom two for several weeks, which means that the show knew what it was doing with the ultra-slow version of a pop song which put her in the bottom 2. I think they knew they would have James and Ella in the bottom 2 that week and used it to ramp up James' votes.
When Tulisa ranted "You can't keep voting the joke acts in", how many people though "Well you saved Rylan" - and who went out the following week? Another stroke of XF genius.