Which restriction enzyme would i use?
Remember than Pvu1 cuts in the middle of AmpR, and when you insert your gene you'll be disrupting its function, meaning that any transformed colonies will no longer be able to grow on Amp-containing media. This is why you want to cut with BamH1 - the disruption to the TetR gene is irrelevant, and it leaves Amp resistance in place.

The point of growing on antibiotic-containing media is to select for cells that have taken up your plasmid - cells that haven't can't grow.