Channel Tunnel (Chunnel) drive straight on (usually), takes 40 minutes to France, drive straight off. Fast, but expensive (+25%)
Dover Calais - 75 mins crossing, 3.5 hours on motorways direct to Amersfoort. We normally do this and can make it London - Amersfoort in 7 hours.
Dover Oostend - 3.5 hours crossing, about 2.5 hours to Amersfoort. The boats are not as nice, and the distance/time is about the same.
Harwich Hoek van Holland - about 3.5 hours on the HSS (superb! We went on the bridge last time, like a massive speed boat, all controlled by video consoles and two joysticks. Has two Boeing 747 engines to power the water jet thrusters. Brill!!!!) with about 1 hour to Amersfoort, all motorway.

We usually choose Dover Calais boat if we want to go to SE/SW England, and Harwich Hoek if we want to go to the Midlands/East. Plus we have shares in P & O which makes it a lot cheaper via Calais