I used to love frame locks, but they're unreliable in comparison to an axis or lockback:
Axis > Lockback > Frame > Liner
I only rate the lockback below the axis because you're more likely to accidentally bump it. Another plus to the axis is that it only disengages when pulled away from the blade, so the only time you could possibly accidentally disengage it is when you won't be getting cut by it (and your fingers would need to be out of the blade path, anyhow). Then you have the axis with an added safety, which, short of catastrophic structural failure or gross negligence, should never be possible to accidentally disengage in such a way it could hurt you.
Frame and liner locks are bad because you have to stick a finger in the path of the blade when disengaging it. For this reason, an accidental disengagement will be much more dangerous.