What sort of bike will suit both offroading and onroading I live in an area which is connected to main road by a small lane(worse than mountainous region, I mean it's condition) and the main road is just like a new tarmac surface, the speed breakers are something like road blocks half feet in height and half feet in width with triangular surface. My old bike is an mtb and serves both well but it is heavy any suggestions what I should look for in my new bike.
Check out cyclocross style bicycle.
It does well on the road and light trails.
You can put touring tires on it.  

wiki Cyclo-cross