Here's my threpence
I've posted this a few times now, but:
I love the Euro Tunnel, I just love it. I think every time I've used it I've pulled up, self checked in, and it's offered me the next crossing, no extra charge. I went last year on it at end of July, returned start of August, £70 return. I think that's pretty good. I've never had to queue up as long as I have for a ferry. No fannying about with strapping your bike down. No dicking about getting valuables etc and carrying them around for 2hours. No having to remember how to get back to you deck where your bike is. (and just for me, no sea sickness!)
Only downside for bike riders is there's no seating and the floors are obviously dirty, and not much to look at - still, it's only 30minutes or so.