Steps tracker

I have a Garmin Vivofit which I really like. You can purchase a chest strap that pairs with the watch to track calories burnt for exercise other than walking.

I really like my basis peak, as it's a heart rate monitor without the strap. And waterproof! I don't like that it's not connected to MFP but I can live with that! It's really helped me knowing my calorie burn for the day, and on average etc.

I don't get on with chest straps (tried for two years but all seem to cause skin rashes) so was waiting to get a basis peak. 9 months after launch they still aren't available in Singapore so I got a Fitbit Charge HR about 2 weeks ago. I really like this and it seems to be fairly accurate for pulse, steps and flights climbed. I was originally put off by reports of skin sensitivities, but if I clean it daily, I don't have problems.
The iPhone connectivity is wonderful and set up was easy, but the battery life never exceeds 4-days for me even without the alarms set.

Depending on what you're using it for. If it's just normal daily activity, a Fitbit or any other arm base activity monitor will be fine, but if you're doing cardio exercises, something with a chest strap is the better choice.