Fire secondary is always more fire. So while yes it does more "damage". You may lack a secondary you would like to have. If this just going live in a fire farm all day. It's fine. Fire & Cold are also two least resisted damage types by mobs on average in CoH. There was several folks who did data collecting on this on live and on HC.
List for least to most resisted goes as
Fire, Cold, Negative, Psionic, Energy, Toxic, Smashing, Lethal.
Mind you specific mobs may have higher reists/defenses to those thing. But on average that's what order is.