I was looking to replace my Garmin 305 with something smaller and was looking at the 210 vs. the 10. The 110 got poor reviews so I didn't consider it, and the 610 was out of my price range. Here's what I found when looking:
10...
-5 hours of battery life on GPS
-Can only display one type of pace (I forget which it is, current, lap or average?)
-Displays 2 fields at a time on the screen, you scroll through to see each pair
-has an interval function
-Cheapest Garmin available ($129 I think?)
210...
-8 hours of battery life on GPS
-Can display current, average OR lap pace
-Displays time, pace and distance on the screen
-Pretty sure it has an interval function
-Costs about $200 (I got mine for $150 thanks to a rebate offer)
I went with the 210 for the longer battery life and more pace options. These two features alone were worth the extra money for me...the battery life issue really made the decision. I was training for the WDW marathon at the time and knew it would take me more than 5 hours since I stop for tons of pictures. I LOVE the 210, except for the charger...it can be finicky at times.
Check out
www.dcrainmaker.com ...really detailed reviews of all the Garmins here. Good luck!