Just thought Id share my experience printing with PET. In a word: it ROCKS;
I bought a spool to experiment printing some transparent vases and stuff, but little did I realize PET is simply an awesome material all round.
It prints easier than both ABS and PLA; no curling at all, no warping, no problems, even with huge prints. I can print this at tremendous speeds, 100mm/s without issue. In fact, strangely, the faster I print, the more transparent the result. Dont ask me why. Its amazing in its ability to print overhangs. Even 60 degree or so when I forgot to enable support printed just fine (!) although that was with thick layers.
It adheres extremely well to a (coated) glass plate at moderate temperature, and pops off once its cold.
The resulting print is as stiff as PLA, but as strong as ABS. Almost as strong as Nylon.
Only downside I see is that you cant smooth it with acetone and even painting may be tricky (havent tried yet). And you may not want all your objects to be (semi) transparent 
As far as transparency goes; you will want a (very) wide nozzle and as thick layers as you can (50% of nozzle width) if you really want transparency. Using a 0.4mm nozzle its more white than transparent, with a 0.6mm transparency its vastly improved. 1mm is probably even better. And as mentioned, for some reason printing faster also helps.
For the record; I print @225C on to a glass bed @100C (but Im sure 70C is enough, objects dont come loose until its at room temperature). Fan is at 100% after the first few layers.