Originally Posted by _ForceD_

bigd -- Seriously...you are sort of asking about a comparison between apples and...Sharpie markers. Think of it this way. A Garmin device is a GPS receiver that will tell you where you have been, and where you are. It'll measure speed and distance for you. And, depending on the specific device...may give you all sorts of other data for analysis. Things like average speed, RPM, Watts, calories, etc. Now...Strava, as a web service, has been described as like a "Facebook for athletes." You can have "friends" and "follow" other athletes just like on Facebook. On the actual Facebook, you can upload pictures from cameras, other devices, "check-in status," etc. So, in that same vein, you can use the Garmin device to upload a workout you recorded to Strava. OR...you can use your smartphone and the Strava app. Your smartphone has a GPS receiver. One thing to keep in mind...Strava has a 'free' version, and an upgraded version ("Summit") that requires a monthly fee. But...you have access to more of their services.

Hope that helps.

Dan