What Line?
Scottd,
If you get a multi-tip line, then you can still use polyleaders if you should decide to. If you buy just a floater, then you have no option for using a sink-tip if you wanted to.
As for which style of line? There are numerous discussions in the archives dealing with long line versus short line systems. Use that information to determine which will overall best fit with the fishing conditions you are most likely to fish. Based upon that info, pick your style of line and then find an instructor that is qualified in the style of casting that matches with that line.
Flylines, regardless of the style, do not teach people bad habits. People do! To avoid this problem, avail yourself of QUALIFIED instruction. If you choose to teach yourself, then expect to make a lot of mistakes. Learning any style of Speycasting requires commitment. To put a perspective on what is involved, think of learning to cast a single handed flyrod with a standard overhead cast. Compared to a Speycast, the overhead cast is two-dimensional. A Speycast on the other hand, is THREE-dimensional - the use of the water's surface being the third dimension. Easy to learn? Not quite. Like any wothwhile skill, it takes some amount of personal investment. Worth it? You betcha!