I think GTP is better... but I might add that I'm currently on course to start on a GTP placement from September (in Physics).
Sparkley - what subject? And you still need to be accepted at a uni for GTP, as they will be the one with the salary grant! But you have to make a choice before you go to a GTP university interview often, they don't like to interview people who have a PGCE offer in some places and require you to turn it down first. Check if this is the case where you are! Hopefully it isn't! If it is though... try to find out how likely it is you'll get the GTP place.
I'd go for GTP if you think your chances are good. If you aren't maths or science, then GTP is more money (if you are, it makes little difference). And as for being thrown in at the deep end... if you are doing a GTP, surely you have past teaching experience? That's generally a requirement for the GTP.