I feel for you, and you'll do what's best for you and your pup…My ex bf had adopted a bullmastiff/shepherd mix from the animal protective league, we were told he was dominant, difficult to walk on a leash, not well behaved in the home..what fools we were for believing all this..he was great in the home, great with humans, and great on a leash..in the back fenced in yard, until he saw another dog...he wasn't dominant, he was viscious..one particular day Max bent the gate door, and he bolted..right for a shepherd walking with his owner..scared us all, the police were called and we were given a warning..we paid their vet bill, and worked with Max...You could tell his previous owners had him properly trained..he listened so well, so well..until he saw a dog...we had taken him to many ball parks where my son was playing, children would climb all over him, he loved it..but with another dog, we held the leash tight, and kept him close..One unfortunate night, at a ball park, Max broke the leash out of my ex's hand and tore for a toy poodle, took it in his mouth..it was horrific..he did not kill the poodle, cut his ear up though...I think there is a difference between viscious and aggressive...
Anyhow, after speaking with several, and being advised this behavior would not change, he was older and his blood lust was deep, my ex chose for the safety of others, we could not keep him.
In July of '07 after weeks of my children begging for another dog, I caved..my ex talked endlessly to my children about the responsibilites of a puppy...training a puppy, etc., etc., we chose to adopt through a local animal rescue..and found an adorable black shep/husky litter that we went to visit..and in the crate next to these two little girls was this little brown dog with white paws..and he was so damn cute..every time my daughter walked near the crate..he got up and ran figures 8s..that was it..we were talking this little brown brother home..we had done the basic, come, sit ..stay..etc., training, and he'd listen here and there..but not like a shep would.. We kept Sultan crated during the day unless someone was home, and then for short periods of time when someone wasn't home..and OMG...the destruction...It's been a year and a half now..and now I've learned I have a B-mix..and thank you all for being here, I've read more in the last few weeks and learned more..and I guess I'm fortunate, I have a fenced back yard that he plays in all day..and since he's mixed, he tolerates the cold (not the rain) I'm also not home much, I work two jobs to survive the no health insurance issue, so Sultan is home most days alone and at night with the kids here and there, but he's adjusted to the schedules, and when I'm home, we play...
I had spent many nights crying over this pup...but he's mine, and I'm his...
You'll do what's best for all of you...
I'm not a fan of them. When I see someone walking a dog that wears a prong collar, all I think about is whether the owner is substituting a prong collar for well directed training. 
