660cc alto is gud in sense of 2nd or 3rd car if talking abt usage, its obviously not in coparission with santro which is a gud family car with 1000cc MpFi engine, and runs like hell on cng with Ac and gives best mileage if concerning any 1000cc car in market right now,
although its ur personal choice, in my openion santro has no comparission with Alto 660 cc .......
few things like spares not available like that of santro which is a market car.
cng will be big issue in 660 cc alto .
mileage of 660 cc car will be fine if u drive at like 60 to 70 max, but if u cross 70 km/hr , it will eat like a 1800cc car, and thats a fact, example is mini pajero, or any car u take , power to weigh ratio does matters in this regards.
resale of alto will never be like that of santro in upcoming few years cos santro has made its market but alto have to take some time,
but besides all that ........ there is gud price difference in both cars also, alto is 2002 model one person bought for 425 k ...... santro u can have 2005 in 400-450 k depending on condition .......
else choice is urz bro ...... do some research before thinking of any out of market car .
my vote is for santro for sure ..........
Best of luck