I moved to the SE for a London job about 18mths ago.
I was originally looking around Haywards Heath but due to having to initially rent and having dogs, we ended up in a small village near Tonbridge.
We ended up buying here as we quite liked the village. It is not good MTB country, hardly any bridleways and pretty flat but it is really good road biking.
I bike to the train station, 15mins, get the train into London Bridge 50mins, and walk 15mins to my office. It works out about 1hr 15 - 1hr 20 door to door. Which is personally about my limit.
Sevenoaks is noticeably more expensive than Tonbridge, 15mins closer to London makes a big difference to house prices.
If you have to drive to train station then don't forget car parking costs of about £5 a day on top of your train fare.
From what I have been told from others, the SE Trains that run in Kent give a better service than the Southern trains that cover Sussex.