I'll give a reason for each as well, otherwise it would all be a bit pointless.
Series 1
Favourite: Saira. It was close between her and Miriam, but whilst I rated Miriam more on performance, Saira had the edge on personality! And I loved how she was just never ashamed of herself.
Least favourite: Paul. He struck me as being a really unpleasant person. He hid behind his pseudo-honourable 'I don't want to say who should be fired', which was just pathetic really, business is business. In other circumstances, I'd say that made him nice, but he was aggressive, arrogant and had an appalling attitude towards his female colleagues - obviously Saira was the one that he had the biggest issue with, but I think that Miriam and Rachel both felt that he looked at them in quite a sexist manner. In addition to that, he was completely unable to control his emotions - I find it quite comical to compare his behaviour at 34 with that of 16-year-old Zara in YA2.
Series 2
Favourite: Ruth. In addition to being one of the best task performers of all time, she had a lovely honesty and integrity to her which I always appreciate.
Least favourite: Syed, for the exact reverse of the reasons that I like Ruth. He had a dishonesty and untrustworthiness to him. I like people who are completely frank, and don't try to weasel out of things.
Series 3
Favourite: Sophie. This was a difficult one to choose, and I chose Sophie in the end because whilst I didn't rate her on the tasks, I did appreciate her moral and ethical values. Possibly she was a bit too naive, but I think if she could find a balance between the two, business needs more people like her.
Least favourite: It's very tempting to say Katie, but that wouldn't be fair since most of my dislike for her is for things that have occurred since The Apprentice. So I'm going to say Rory, because he was a dreadful manager and a dreadful person, pretty much.
Series 4
Favourite: I didn't love anyone in this series, but I suppose I'd say Sara. I wanted her to win, but also I thought she was a decent person.
Least favourite: Jenny. Bully.
Series 5
Favourite: Yasmina. Talented, honest, straight-talking, much like Ruth.
Least favourite: Philip. Horrible shouty man, who had a chip on his shoulder about poor Lorraine for no reason at all.
JA1
Favourite: This is a hard one because I really liked nearly all of the characters in this series, but if I had to pick a favourite, based just on personality and not task performance, I think I would go for Tim, because he seemed like a lot of fun.
Least favourite: Rhys. Irritating, whining schoolboy.
Series 6
Favourite: This was another hard one to choose, but I'm actually going for Sandeesh, as I liked her spirit and she seemed like a really genuine person. Also, I think it must be said that she is one of the most beautiful women that they have ever had on the show. It's really rare for someone of her ethnicity to have green eyes, and it worked really well. I don't usually comment that much on what people look like, but I just thought Sandeesh looked stunning.
Least favourite: It is really close between Dan and Stella actually. I thought Stella was horrible, but I'm going to have to go for Dan, just because Stella was able to work with people regardless of her personality and Dan just wasn't. It is probably becoming clear that I really don't like aggressive men - or women for that matter, but I think men tend to come across as a bit more threatening in that capacity than women do.
Series 7
Favourite: Again, it was a difficult choice between a few people, but I'm going to have to go with Helen, just because I admire people who work that hard, and produce results.
Least favourite: Jim, because I felt he was a bit of a snake. Wasn't an exceptional performer, bigged himself up to come across as much better than he really was and in the end had a stupid business plan.
YA2
Favourite: Zara, and I can't really see the point of going into why, because we've had this conversation to death. If anyone wants me to I'll clarify, but I think everyone here already knows why Zara was my favourite, not just in this series but in the whole Apprentice franchise.
Least favourite: Harry M. I hate smug, arrogant, slimy people like him. To his credit, he didn't deserve to lose every task, but he also didn't deserve to get as far as Week 7. He had awful people skills, took any criticism of his ideas as a personal attack, and when he was Project Manager may as well have been in a team by himself. I think it's very telling that the other Harry, who is normally quite guarded about his personal feelings towards people, is completely open about the fact that he can't stand him.
Series 8
Favourite: Gabrielle. I think probably the most likeable candidate to ever be on the show!
Least favourite: Azhar. I don't think he did anything amazing on any of the tasks, and was another of those people who thought they were much better than they actually were. Forever known as 'Mr Strategy'.
YA3
Favourite: Ooh, it's so close between Lucy and Patrick... I think I'll have to go with Lucy though. She stayed very calm and in control, and she was quite a diplomat in a group (like when she tried to calm Amy and David down for the sake of winning the task).
Least favourite: Actually, most of the people in this series seemed really nice generally. I'll have to say Maria as she was quite difficult to work with, but to her credit she seemed very popular with the other candidates - both times that she was in the boardroom, the others in the house were really hopeful that she'd return. In interviews since she has seemed like a genuinely lovely girl, so I feel quite bad for doing this - but there is no one else I could justifiably give that label to. If I were to rank all my least favourites in order though, she'd definitely come last.
Series 9
Favourite: Jaz. Genuinely loved her! Even though she went in the first task, she really made her mark. I'd love Jaz to be my mate - we'd go down the pub and have a laugh!
Least favourite: I think Jordan. He was a strong task performer, but I completely agree with what Claude said to him. He had no right to go about selling shares for a business that was not his own, and besides he broke the rules by not allowing Lord Sugar 50% equity. He was never going to win simply because of the terms of his business plan, and by going on the show he took the opportunity away from some other man who might have had a really great business plan. So yeah... I really object to what Jordan did.