You would most certainly be wise to avoid the non union or weak union ones for just that reason. Stronger Unions tend to protect their employees. AA Pilots have limits that are actually similar to CAP 371 with a certain amount of circadian rythm protection (which we are hoping to improve on this time around).
However, even without union protection the 16 hour duty limit, is overlaid usually by an 8 hour flight limit. So you have to be really poorly managed or abusive to hit the 16 hour limit (and many airlines are).
At the top of the list for abusive scheduling practices would be the nonsked or charter operators. And that holds true on both sides of the Atlantic. Its just the nature of the beast. However, accident statistics have not really pointed to worse safety records, atleast the last time I looked which was about 2 years ago.
And good scheduling practices do not always make for more rested crews. The airlines that pay their crews well and treat them better may allow some of them to pack more "living" into their life resulting in their being more fatigued than the person who is chained to his aircraft. Fatigue is a very funny thing to try and pin down.
Many of the objections to copairings wind up being the disruption of the crews. Who are we laying over with etc. When we used to pair for the whole month, you really got to know each other and the layovers became very enjoyable. That goes away when you change crews every leg, and certainly detracts from the enjoyment of the job, but it can be argued that non copairing improves safety because it tends to make people more by the book. When you fly together for an extended period of time, despite the best efforts you can drift away from SOPs in the free and easy work envirnment as you do what "just works." When you fly the first time all you have is SOPs... Now you get into the discussion of the value of SOPs...
Cheers
Wino