What do you mean by better? For the price, I'm not sure. The 550ti is way stronger though. I wouldn't get either. 7770 is a better option.
^Agreed. 7770>550ti>610 no matter what memory they have on board.
Well if you want to run a few monitors for productivity, and have no interest in games, the 610 is "better"
If you want to play more than facebook games, however, don't touch the 610 with a *insert colloquialism here*.
The stronger card is going to be the 550Ti 10/10. The Nvidia cards with 2nd numbers in a series that are 1, 2, 3, or even 4 are meant as home theater cards and will not be worthwhile unless those are the only things you are trying to accomplish. I would say the 7770 is the best value as well.