For years I've used nothing but 6# P-line Fluorocarbon or Fluoroclear. I was thinking about asking this same question a few days ago because it sucks to have to change expensive line so much. I wanted to test out the braided line because it could last for years. I have a few other friends that stand by the braided regardless.
Crappieguy, I've never really known how deep I am when I'm fishing. What I do is let line out, if I don't get bites I let some more out until I start catching or getting hits. The key thing I do is count how far I let out or real in so I have an idea of where I am by how much line I have out. Because I've experienced your same issue with the different lines creating different depths at different speeds I thought this way worked out great for me. I've always felt there are just too many variables to REALLY tell your exact depth when trolling.