Going to the website and doing their little "help me pick" questionnaire is a great idea. If you go to the link @Montepulciano gave you and scroll down a bit, you'll see a pink Compare Trackers button that you can click on, and then you can click on different trackers to see a chart with features.

Cost definitely plays a part, but they are on sale for a while!

Some key points to consider though:

1) Do you want a tracker you wear on your wrist, or one that clips on?
2) Do you want a tracker with an HR monitor?
3) Do you want a tracker that counts floors in addition to steps?
4) Do you want phone notifications on your wrist? Make sure your phone is compatible first by going here: https://www.fitbit.com/devices

All the wrist trackers except the Surge have a replaceable band now, which was the main complaint I've seen for the older models. Any problem with the band meant you had to try to glue it together or replace the device if it was out of warranty.

I have the original Flex and recently upgraded to the Blaze. The Blaze is a little big on my wrist, but I like it so far. When my flex eventually gives up on me, I'll get a Charge 2 or Alta to wear at night/when I need something smaller.

~Lyssa