huwai e3131 b vs airtel huwai e1731

I am confused to choose between two.
e3131 @1950 attracting feature is 21 mbps
airtel e1731 @1200 -7.2 mbps

I resides in North U.P near delhi and want to purchase a datacard according to scope of 4g in future.however someone suggested me to pick airtel because in future there would be good h/w device to handle 4g.but i am afraid about unlocking procedure of airtel if it would not work for other sim's.

I would like to know whether e3131b can handle 4g data speed in future and is it faster than other devices like micromax or airtel e1731.

Help me out to pick the best one according to the constraints.
i don't have wifi requirement

Thanks in advance