I use a bunch of different 'standard" fluoro lines. I use Seaguar Red Label for heavier applications such as leader butts and mids or tippets when streamer fishing. The red label is pretty cheap and at higher diameters and lb test, it works fine. Other lines I use are P-Line 100% Fluoro, and Seaguar Invisx for tippets for most nymphing. I also use Red Wing Phantom Fluoro leader material for very fine tippets. When it's all said and done I use a TON of P-Line in 4, 6 and 8lb.
All work well and I will likely NEVER pay for fly fishing specific fluoro. $15-30 will get you a heck of a lot of fluoro spooled for conventional gear.
One brand I avoid is Berkely Vanish, I had very bad results when I tried it. The knot strength was very poor. It may have have been improved in the years since I last tried it, but I've had such good results with the others that I have no reason to try it again.