antenna for Garmin GPS in C172 or C152

Looking ( yeh I know I have been looking a lot) at buying a Garmin GPS (
probably a 96C), and they have 2 types of external antenna, one has like a
suction cup on it and the other has a magnet.). Just wondered what type is
best and where the best place is to locate the antenna . I would have
guessed the back window would have the least obstructed view, but then I
have to run the cable from the yoke to the back window which sounds a bit
messy. Will the front screen be OK? ( I am only a renter, so I cant lay any
cables permanently). What do other folks here do with their antenna? I am a
bit wary of the magnet idea in case it affects the compass ... I dont want
to rely totally on GPS.
terry