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.
I'm in similar situation. My solution (since my entire trip is 20 miles one way and only 3 miles are forest trail) is to bear the bumpiness (with stock carbonfork) by putting 700x 35 tires on Trek 7.5 FX which is a road bike biased hybrid. If you go with smaller wheels it gets bumpier. If you go with wider tires than you suffer on pavement.
And yes, as the elders say, if you want to shell out some $ (as opposed to getting decent used bike on Craigslist) buy a cyclocross bike!