I can't speak for the Garrett, but I have both the Cortez and the DeLeon. Picked both of them up used and haven't had a problem with either. That said, If I were in your shoes I'd look hard at the differences in the bells and whistles on each machine versus the price. The biggest downside in my mind on the two Tesoro detectors concerns ground balancing. The Cortez only ground balances in the all metal mode, the discrimination mode is factory preset. The DeLeon is factory preset in both modes. Most of my detecting is in mild soil and both machines work very well here. The Cortez display is a bit small and can be a bit hard to read. On the plus side, they're both coin magnets in my soil and are a delight to swing as the weight is pretty light. I understand the Garrett is submersible to shallow depths which would be a big plus around creeks and beaches.
Of course you could always buy one of each, after all, anything worth having is worth having two of. Good luck in whatever you decide.
luvsdux