Both systems are very reliable; though, you may favor the advantages of one system over the other, depending on your need.
The Flame Front Generator (F.F.G) is easier to access for maintenance, as all operating components are at the base, and it has the option of a manual ignitor at base; yet, it needs regular maintenance to ensure reliable operation.
The High Energy Ignition (H.E.I) is easier to operate and requires a less complex piping system; nevertheless, components must be replaced over time, requiring a shutdown of the flare.