I must admit I am sometimes divided between C4 & BBC.
Though I hadn't purposely taken an interest it seemed C4, on hindsight, had slightly better pre race interviews, I guess like anything it's who is performing well at the time. I would imagine who they are interviewing helps somewhat, Jimmy Fortune seems to come across well in an interview, though I have only seen a couple with him.
I think out of Carson & Francome, I prefer the character of the later to be honest and can find him quite amusing sometimes. I have never heard Carson say anything on jump racing to be honest, and I suppose as one comes from the jumps and the other the flat this may make a slight difference to what their analysis maybe or, how they put it across, given the type of race. I'm only guessing on that as I don't know either of them or the technicalities of presenting for that matter.