Mage earth pet was traditionally king tank of pets. Other mage pets are situational tool box... for a while, fire pets were favoured lower level but almost never seen above 50 (funny how scaling and changes impact usage of things). So many changes to pet behaviour, AAs and gear to strengthen them (as well as improved spell power at low levels, and status in current endgame tuning-wise)... mage class would always have been a top-population class if they had been this good originally.
Beastlord pets were really strong into the 50s, and have had kind of a mixed amount of attention/developer love post luclin.
Necro pets have some up and down with the tanking thing... but were always supposed to be somewhat strong (aggro kiting was the less forseen tactic. fear kiting was much bigger once upon a time.... rogue pet backstabs the feared mob).
These are the true pet classes. SK, Druid and Shaman got a "flavour" pet that was much lower level, so really just a dot spell that followed you around. Considering everything else these classes has or can do... if they had even Necro warrior quality of pets that would be a pretty major boost (though not that useful to an SK... a rogue pet would be moreso).
Enchanter shiny bob wasn't a true pet until AAs made it controllable. It remains glass in most situations though.
Cleric hammer pet is pretty bad. Was always painful grouping with a new cleric that finally got to the level to mem that spell. Mems it, tries it out and realizes how little benefit is gained from using the spell gem slot.