Companions

Disclaimer: I am not THE authority regarding companions, however, I've done an excessive amount of research and will share some of what I have learned with you -

Although companions can be paraded around Neverwinter as status symbols, they are an important part of your character's make-up and should be given some serious consideration when selecting. Your needs will change as you level and depending on the choices you make (PvP, soloing, dungeons, etc).

The easiest way to cover them is to start at the beginning...

Below Level 60 - Solo Questing

Companions can be defenders (tanks), strikers (dps), controllers (crowd control), healers and augments. Your first one should be what you aren't, for example:

If you are/pick a -
GWF - Healer, Controller, Defender
GF - Healer, Striker, Controller
CW - Defender, Healer, Controller
HR - Defender, Healer, Controller
TR - Defender, Healer, Controller
DC - Striker, Defender, Controller

Dungeons:

An augment companion won't really come in handy until you are either level 60 or doing dungeons since it will not fight for you. However, an augment companion is just what it sounds like - anything that you give to it via gear, enchantments and runestones are stats that YOU get when you are using it.

The reasons why players use an augment companion in dungeons are very simple.

1. They won't steal aggro
2. They won't accidentally blunder into a bunch of mobs and get you killed

60 and above - Companion Choices

By now, you should have narrowed down which companions are best for your class. At level 60, you should only be using two of them consistently - 1 for solo play and 1 for dungeons. The rest of your companions should be there only for the stats they bring.

Runestones:

For your soloing companion - if you have the right slots, I highly recommend the combination of (lesser) indominatable, bonding and serene. You cannot use these three on your augment companions (Well you can...but they won't do anything for you)
If you have a defensive slot - an Eldritch runestone is a good choice as it will give you a percentage of your companions stats whenever you are using them.

Gear:
I load my companions with epics that I won't wear for two reasons.
1. It helps keep my companion alive....occasionally.
2. It's portable wealth. If I need to salvage it for some AD in the future, it's right there.

Leveling Your Companion:
Spend the time to level them to their maximum potential. They will die a lot - but they'll learn.

White/Green/Blue/Purple?

Let's face it - upgrading your companion is expensive and should not be done frivolously (although I have done that a lot). My rule of thumb now, after months of playing, is this:

1. Max them to their full original potential and use them. If they are good and the stats help me...then I level them to blue.
2. If after that, I'm reasonably sure that I'll keep them in my 5 slot arsenal permanently, I invest the AD to make them purple.

And finally -

Keep an eye on in-game promotions. They can easily slip by you. Some of my best companions were freebies and I found them by going here:
http://neverwinter.gamepedia.com/Promotional_Item_Giveaway_Codes

For Augument type companions, you want to stick with the usual runes: Eldritch, profane, arcane, etc. I generally use whatever I'm deficient in since these stats will stack with your own. An Eldritch rune in a defensive slot will further increase your stats since this stacks an additional percentage of the companions stats.

For all other companions, I use the combination of indominatble, sincere and bonding runes as long as the slots needed are available. You may choose to put an Eldritch in a defensive slot on these as well if you want...but since you'll only be using this companion for soloing and at lower levels, your augment companion will be better for you stat-wise.

At level 70 - you want to invest well in your augment companion in regard to gear, runes and enchantments. The rest of your companions are there just for the active bonus they can bring

Seth of Hope