I've had both the Jawbone Up and now have the Fitbit Surge. I absolutely loved my Up, but two big things come into play:
1 - Display. The only way to see how I was doing was to sync my jawbone to my phone, and I didn't always have my phone with me. With my Fitbit I get the display that continuously updates with my steps. May not be a big deal to some, but for me it's about motivation and accountability, and being able to look down and see where I'm at is a big deal to me.
2 - My Up eventually broke, as the stress of removing it and putting it on for showering, etc. was just too much after a while. I was VERY careful when putting it on and taking it off, but even then I only got 8 months out of it before the bending snapped it inside the rubber. Having a watchband on my Surge has removed that problem, though I'm still super careful with it.
Other than those two things, I had no issues with my Up and thought it was lights out. I also had one of the original versions of the Up, so perhaps the band has made big strides in its durability. Still, though, I much prefer my Surge.