Bebop is very different from Firefly imo. They're both good, but I wouldn't say to watch one over the other. I can't directly compare them like that.

Bebop is smooth and classy, more focused on music and choreography. Firefly is way more grounded and physical; lots of greebled grimy tools, machinery, carts.

You can see a similar divide in the themes. Firefly is way more rural, frontier type western. They get rid of small-town despots and help trading outposts under siege, because they're the only help around. Bebop is the end of the wild west: they all have stories about the real west, but that era is over. Cities are growing, the government starts playing a role, outlaws are on the run. The heroes are struggling to let go of the past and find their place in this new world.

I also want to shout out Outlaw Star, released in the shadow of Bebop. It's not western at all, a bit messier in its theme, but still a lot of fun.