I understand that you get more options on the Win Platform. If your
looking for a specific option that you intend to use alot, then you will
certainly want to factor that in when you make your OS choice.
But just having lots of options in itself is not, in itself, a good
reason to base your choice on. The Mac platforms tend to be more
quicktime based, but your encoding options are varied allowing you to
create delivery formats for a range of end users, from tiny Ipod size
video to lossless formats that most any other platform will handle with
no difficulty. Of course you have the standard DVD export routines, and
you also have flash video export routines.
For import concerns, I have found a program called Visual Hub to be
quite useful in conversions. I've found it to be able to quickly convert
most everything I throw it at, specifically those xvid and divx file
that tend to be problematic for NLE's on both platforms.