The only contestant I've truly disliked was Iain Stirling, but I didn't finish Series 8 because the whole casting seemed off. Sterling and Lou Sanders were far too similar, but he just took it too far (that first group task was painful to watch). Joe Thomas and Sian Gibson were okay but not the most entertaining in the tasks but sank into the background in studio segments because Sterling and Sanders were so loud, and Paul Sinha was effectively useless both in tasks and in studio, which I suppose is understandable given he was diagnosed with Parkinson's just after they finished filming.
I might go back to it at some point, but after a few episodes I ended up binning it.