Monster Manual Creature Companions

[Duscara]

In regards to the Monster Manuals, I have the Prologue and Volumes 1, 2, and 3. I want to get a Creature Companion from the Monster Manual.

Assuming I don't get any more, here are all of the ones rewarded by the Monster Manual available to me:

Forest Spiderling (Kill 12,000 spiders over at least 80 types)

Fruit Bat (Kill 3,500 bats over at least 10 types)

Gray-tipped Rust Monster (Kill 3,500 rust monsters over at least 20 types)

Obsidian Earth Elemental (Kill 7,000 earth elementals over at least 24 types)

Violet Wraith (Kill 7,000 wraiths over at least 30 types)

Blue Fire Elemental (Kill 1,600 fire elementals)

Chaos Beholderling (Kill 1,600 beholders)

Which of those is the easiest one to obtain? My best guess would be the Fire Elemental, given that I don't have to kill as many of those as I do the other things, and I'm pretty sure Fire Elementals are easier to kill than beholders, though it could vary.

My account type is Premium, by the way.

And no, buying one from the DDO Store is not an option.

[Annex]

If I recall correctly, I ended up earning the Blue Fire Elemental first.

Taming the Flames includes something like 40 Fire Elementals and some of them respawn. If you run it on Casual with a decent Fire Resist item, you could probably earn the Blue Fire Elemental pet in a long afternoon. A level 7 Resist Fire Potion (20 Fire Resistance) might offer enough protection on Casual or Normal, especially if stacked with 5 points (or more) of Guild Fire Resistance.