Umm, I am not too sure whether unlocked 3g wifi
routers are available in India, and on how they behave with mtnl.
But mtnl 3g usb stick is just the same as reliance netconnect's usb stick.
Mtnl 3g has speeds of around 2.5 mbpsand unlimited data with no fup for 1650 bucks a month.
http://mtnldelhi.in/dolphin/index.php/3g-prepaid-plans
However, do check the 3g signal strength in your house, by buying a prepaid sim, and putting some 50 _ 100 bucks in it. You will need a 3g/hsdpa capable cell phone to test 3g signals. If you are happy with the speed, then go ahead and buy usb stick. Browse around the mtnl 3g forums.
however, if you are not happy with 3g, then stick with triband. just buy a
D-Link,
Linksys or
Belkin router. A decent one should cost you around 1500 _ 2000 bucks. Connect your mtnl
adsl modem to it and enjoy wifi. Get one of the N150s.
There will be absolutely no degradation in speeds given the size of your place.