As long as I've been making seed bead jewelry I've been using power pro as my thread, and I love it the only problem is when I use lighter colored beads since power pro is a dark green color. As you can see in the picture below it doesn't look so nice against the white beads.
Fireline on the other hand comes in several different colors including crystal which is almost invisible against the white beads which you'll see in the next picture.
It looks a lot nicer with the white beads. Both threads work up pretty much exactly the same. The only difference is the Fireline seems a little slippery to me but that will just take some getting use to since Fireline is more of a plastic (monofilament) and power pro is a thread like line. Also power pro frays at the end when it's cut which can make it difficult to get through the eye of your needle while Fireline passes right through. I will continue to use power pro with most of my projects but in the case that I'm using lighter colored beads I'll be using the Fireline. Hope this helped you if your looking to try a new thread :)
Edit: I've actually now switched over to using fireline only. I tried it out a bit more after this post and decided I liked it better because it slips through the beads a lot easier and causes less tangles.
Here's a comparison shot of the two samples.