My advice would be to go into your favourite cycle store (mine is Brixton Cycles) and to get as much advice on the various bikes and to road test as many of them as you can. If, like me, you cycle quite a bit and you intend keeping your bike for many years it's worth buying new. Otherwise, buy a good secondhand one. Remember: unless you want to lose your bike to thieves...spend about 10% of the cost of a new bike on good quality locks...sounds expensive, but saves a whole lot of expense, hassle and heartache later on. Happy riding!