Hydrocodone addiction vs heroin addiction, which is more dangerous?

Same: Both prescription and illegal drug addiction are dangerous.

Same difference: It doesn't make an iota of difference as both are opiates and have the same mechanism of action in the brain. Many factors can make one person's opiate use more dangerous than another's use such as - amount of drug used, frequency of use and method of use (e.g. Whether oral or by shooting up). If you are struggling with addiction to either of these, please seek help asap. Good luck.