I don't use barbed wire because we have tons of different types of fencing products available in this area. I have RAMM fencing actually... BUT, years ago I boarded at a neighbors house, it used to be a cattle ranch so the fence that was up, was rusted barbed wire and my horse at the time was a 3 year old. NEVER HAD AN ISSUE. The trick is, you maintain a fence like that CAREFULLY, you walk it after EVERY rain, every windstorm, every snow... you make sure it's taught and secure.
I'm not saying it's the ideal fence. I would avoid it if I could. I have actually seen more injuries caused by electric fencing, it's come loose and the horses have gotten tangled or the horses have run through it and it's been a thicker than norm wire.
BUT I've seen some pretty bad injuries from wooden fences too, where the horse has kicked through the fence and scraped his leg really badly. I've seen a horse kick a metal gate and slice a tendon...
That being said... I'm not sure what the SAFEST fencing is. My neighbor has horses in barbed wire, he's never had an accident. Will he someday? Maybe...
Just try your best to keep your fence safe. If you have the option to go electric over barbed wire, do it. If you can do wood over electric... go for it, if you can go w/ a rubber fence over a wood fence... hey, more power to ya!
Just try to keep your horses safe. If you do that, and they still get hurt, well... it happens... just know you tried your best to keep them safe....
"Be a best friend, tell the truth, and overuse I love you
Go to work, do your best, don't outsmart your common sense
Never let your prayin knees get lazy
And love like crazy"