mostly train. Some from Whitstable on standard trains (but see below), some from Canterbury (about six miles ride) on the HST. We've not had a problem getting people on the train, although the chap behind the ticket counter at Whitstable has been less than happy. Bear in mind that the departure times will be from about 8 o'clock to about 4 in the afternoon, although the last of us will probably have to be carried to the station in a litter.
There are two trains an hour from Whitstable to Victoria Station. You can change on to the HST at Faversham, but it costs an extra £3.20, and doesn't save you a lot of time unless you're heading for North London, or catching a train on from Kings Cross, Euston or St. Pancras. Standardsingle fares from Whitstable are expensive. Groupsave/Network Card it.
There's one HST an hour from Canterbury West to St. Pancras which is quick, but costs a lot of money. Groupsave or Network Card a neccessity.
There's two 'standard' trains to Victoria from Canterbury East every hour. They also stop at Selling (about seven miles ride) and Faversham (about eight miles ride). Again, these tickets are expensive.
Some folk do ride home, though.