DH and I used to live in Faversham, which is about 10mins from Canterbury, and DH used to work in Margate. At least once a month, he says "I WISH we'd been smart and bought in Margate instead as we'd be making a killing."
The new Turner Contemporary art gallery is having a tangible, visible regenerative effect on Margate, so if you buy there then you're likely to see you property only go up.
However, it's not going to be an overnight process, and whilst there are massive improvements to it compared to, say, 2 years ago, there are still socio-economic problems.
Between Broadstairs and Ramsgate, I'd be far more inclined to pick Broadstairs. But if you're going to be spending a lot of time in Canterbury, then I would probably lean towards Faversham, Ashford, Whitstable and even Canterbury itself. Faversham very pretty market town, good schools, Ashford much much bigger (3 times as big as Canterbury) and not quite as nice but fast train to London is amazing. Whitstable very quaint and pretty seaside town, but lots of London second homes there which has priced locals out a bit.
HTH!