I've owned a lot of these...my thoughts on each:
Fitbit One
Not technically a band, but my thoughts here transfer well enough to the Charge / Charge HR. I'll be simple - I love Fitbit. The device holds up well, has great battery life (I charge it once a week or so), tracks accurately, is the only device that also tracks altitude gained, their website is decent, their app is multiplatform, they have a nice blend of detailed statistics and motivational / competitive features. They integrate with lots of other products too. They're the market leader for a reason.
Nike FuelBand
Pour one out for the fallen. I loved my FuelBand. It's simple - the data may not be perfectly accurate, "fuel" doesn't really mean anything...but I still loved it. Definitely more motivational than any other tracker out there, and I liked the fact that the more intense your activity, the more points you'll get - running a mile gets you way more fuel than walking a mile. Sadly, Nike no longer sells the FuelBand and is focusing on their app, which is a horrible alternative.
Microsoft Band
Jack of all trades, master of none. The Band can do everything. Steps tracking is reasonably accurate (ends up somewhat near my Fitbit). Heart rate tracking is nice, the built in GPS works pretty well, and the basic smartwatch features are really all I need on that front. It's got some ridiculous bells and whistles I could never care about (UV sensor? Really?). That said, it's a little hard to recommend. The battery life is just terrible, it really needs to be charged every 36 hours or so, it's big and bulky, it's not terribly refined yet, there's absolutely no motivational / competitive aspect. I have a feeling that the 2nd rendition of the Band will be the one to buy.
JawBone Up
I have a curious relationship with the Up. I want to like it. The app is beautiful, I love the smart coach features. It's small and understated which is nice, and the battery lasts a long time...I just...don't like it. It doesn't do anything my Fitbit can't, other than the smart sleep feature, which is a neat idea, except it always wakes me up at the earliest possible time (clearly I sleep restlessly). The stupid cap you have to unplug to sync / charge it is easy to lose (or in my case, your dog to find and eat). Maybe Up3 will be the one, but I dunno.
Overall, I feel like it's a weird time in the fitness band market. The 1st generation is still around and doing well, the 2nd generation products are starting to integrate more advanced features like GPS, heart rate, and notifications, but those features aren't terribly refined yet. It might be worth it to wait for the next round - but if you're buying one now, I'd recommend the Fitbit Charge HR. Best blend of features, accuracy, refinement, and motivation.