I would go for the 610 I think it is a far more capable watch but make sure that you get the new premium HRM with it. If you want a good comparison of the two as gbp11 says above have a look at DCrainmaker's site he has used all these watches and has no axe to grind unlike most magazines etc.
http://www.dcrainmaker.com/2013/11/garmin-forerunner-depth-review.html
The two big things it has that the 610 doesn't are
- Bluetooth for connection to your phone
- usb connection to a computer which is nice and simple to use.
I have a 610 and I upload to my mobile by plugging the ant stick in and using a third party app and use ant+ to transfer to computer - which for me works well.
Overall the 610 has more features to allow you to set up and monitor your workouts whereas the 220 is perhaps a little more user friendly but with less functions.