It depends what you think The Apprentice is looking for. If we were looking for the best person to start their own business - if this were Dragon's Den and Sir Alan were just giving them investment - I'd say Tre was the best choice. If it is someone with potential who needs the guidance and experience it would be Simon, but Sir Alan told Jadine that wasn't what he wanted this time. They are looking for an able employee who can be given a reasonable level of responsibility, but will do what Sir Alan wants - which I think makes Kristina and Lohit the two best candidates.
Katie, apart from any personal feelings people might have of her, would be a liability in PR terms. I don't know what anyone else thought, but in the previous two series, I felt it mattered to Sir Alan that people saw his candidate as admirable, that their 'story' mattered to him, and that he likes seeing himself as this 'Fairy Godfather' turning some young person's life around. Though he may regret his choice last time, I can't believe he would go so far the other way as to hire Katie already on £90,000 a year.
But everything always changes at the interview stage. In theory, since she's so good at manipulation, Katie ought to do very well - and if she is as clever as some people say, though I can't see that myself. Kristina and Tre, going on who did badly in previous series, might struggle - or the interviewers might just take against them.