I usually go speedferries too, but Im usually in a big van with everything inside and its definately cattle class with the attitudes of the ticket office staff etc, they know you paid next to nothing for your ticket, for my van next to nothing equates to about 50-70 return. On the chunnel its usually around 150-200 quid, great that isnt it, public funding helped build it and yet its the most expensive crossing of the lot. It is a nice though, 30 mins and you just ride on, stretch your legs/go the loo and then ride off.
Seafrance is always the second best choice, and usually the cheapest in the port on the day at dover. If you get offered the commercial boat which they do from time to time to fill it up and get more people on the passenger ferry, do it like a shot, you can get a 3 course meal for under a tenner inclusive of drinks (coffee, coke + the usual) and the one I was on had showers etc. At peak times you might have to wait a fair while for space or return at a odd time of the morning, Im not sure what the situation is on a bike, but my van cant get on during peak times as it needs a specially big space.
If you have someone who can book online at the end of a phone thats handy too, I went the port office once for seafrance and they told me the boats were sold out for 4 days (xmas eve, not a option, speedferries refused me boarding on my prebooked ticket as they said I was over their 3.5 tonne limit in their opinion, although they didnt actually weigh me), but my mrs back home managed to buy me a ticket over the net from seafrance's website site for the next sailing. I went back in and spoke to the same guy with my booking number and he seemed a bit shocked that Id booked despite his computer showing no spaces. So maybe the website reserves a certain number or something...
I guess for speedferries there mustnt be quite enough profit to bother with bikers. Cattle class indeed...