Is a current varying output or voltage varying output for a 4-20 mA sensor more reliable for a rocket?
As far as signal integrity, 4-20mA is almost always better. Two reasons why:


Noise is usually less of an issue.
Circuit discontinuity is instantly detected.


As for its use in high g applications, that is more up to the sensor itself, both electrical and mechanical construction. Note if it is more then just a sounding rocket, i.e. entering LEO, then you need to start considering radiation from the environment as well and it's effect on the electronics.