Your requirements : 150cc bike with good mileage.
The best options 1) Honda Unicorn : One of the bikes which gives 55-50 mileage in whatever driving conditons, the other is GS 150r. The engine is the smoothest,vibration free and offers excellent riding position for the driver and riding comfort for the rider and pillion... The monoshock suspension is the best one for our Indian roads..The only con are the looks and waiting period, but other than that this would be the best choice for a 150cc bike
2) Hero Honda Hunk : Shares the same engine as unicorn but the tuning is a little less perfect than the Unicorn's .. Can expect a mileage of 45-50(city) and anything upto 60 (highways). The style is greater and it is the best looking of the above 3 mentioned bikes and comes with digital display. Pillion riding may be a bit uncomfortable but still its a Hero Honda and has good resale value.
3) Bajaj Pulsar : Was the best 150cc bike but is outdated. Go for it just for the pulsar brand and expect a mileage of 45-50(city) and 52-63 (highway). Bajaj products dont have much quality after 2 years..
My choice would be the Unicorn.