I have a fitbit one and I love it. It has a display on the front so you can see how many steps you have done without needing to be on a computer. I found this very useful as it is my goal to do 10,000 steps every day in 2013 (I am on day 293 of my streak - woohoo!) and I wouldn't have been able to ensure this as I have been on holiday twice this year without my computer so I wouldn't have known my step count. The fitbit also has a sleep tracker which is very useful for finding out how long it takes you to get to sleep as well as identifying patterns such as waking in the night. To be completely honest though, this feature is great at the beginning, but once you have the insights, you have them. Although I still do track my sleep on the fitbit I rarely look at the report of it on the website. Another good aspect is the activity tracker. It is a sort of timer function on the fitbit where you start it off, do your exercise, and then it will tell you how many steps you have taken in that segment, how many miles you have travelled and how many calories you have burnt. I don't know for sure, but the Spark one doesn't seem to have this feature.
The fitbit syncs with sparkpeople so you can press a button on your spark fitness page and it pulls the fitness data from your fitbit. It also syncs the other way around with your nutrition tracker - the food you enter onto sparkpeople is sent over to fitbit which I find great as I couldn't get on with the nutrition tracker on the fitbit page. The one on here is much more user friendly. The community on Spark is much better too in my opinion, but I still use both as and I don't have to enter any information twice.
One bonus to the spark one when compared to the fitbit one is that the spark device seems to have a level of waterproof capabilities. The fitbit one doesn't have this at all so you have to take care to not get it wet. There are other models (like the fitbit zip) that is supposed to offer a level of waterproof ability, but you sacrifice some other features for this. You can friend people on the fitbit site though and it ranks your number of weekly steps against your friends and it messages you when you overtake people. This is great for my competitive streak!
Overall, I highly recommend my fitbit. I have never used the spark one so in saying this I am not damning the spark tracker, but a device that encourages you to be more active is awesome! If you have any questions, feel free to PM me, I'd be happy to help you further.
"All the world's a stage,
And all the men and women merely players:
They have their exits and their entrances;
And one man in his time plays many parts."
| Pounds lost: 4.0