Woo hoo! Right up my alley, I'll be glad to give you my suggestions on that topic, Nekoknight.

Relentless, Burst Fire, and Mojo Echo.

Those epics give your companions a chance to do another attack, up to 4 times in a row! It is the best and most satisfying thing to watch your companions do attacks back to back, like watching a combo string from Legend of Legaia or something.

Now, I realize that Relentless only gives you a chance to trigger an additional attack, but that attack is a full powered attack, and can be triggered by any other epic, like Riposte, Vengeance Strike, Crossfire, True Grit, and the witchhunter equivalents. It can also be triggered by First Strike, Overwatch, Repel Boarders, Quickfire, Witchhunter, and any of the other epics.

Now, why not get the other epics? Well, Relentless first. Then if you have room to choose, pick another. Keep in mind, all the PRE emptive strikes only do HALF damage. The counter attacks such as Relentless and such do full damage. A 4x attack is way more powerful than, lets say, a Repel Boarders or First Strike.

My suggestion for epic distribution for ALL companions:

Relentless/Burst Fire/Mojo Echo x2 (depending on companion)

Riposte/Vengeance Strike/Crossfire/True Grit/Witchdoctor equivalents. (Depending on stat of course. If your companion has a very high dodge, give him Riposte.) This also triggers Relentless.

A no strings attached bonus attack depending on how you position your companion. May also trigger Relentless.

Second Chance. This gives you more accuracy, and also has the potential to trigger Relentless.

First Strike/Quick Fire/Witchdoctor equivalent. A half damage attack that is done BEFORE your companion gets hit. May also trigger Relentless.

Repel boarders/Overwatch/Witchdoctor equivalent. A half damage attack done before opponent reaches you. Can also trigger Relentless!

There you have it :) Hope you find this helpful.

Oh my, this is a loaded question.

It seriously depends on your strategy and play style.

Some charge in no holds barred and attack anything and everything in sight.

Some stand back and wait, buff, and let the enemy come to them on their own terms.

First Strike, Riposte, Relentless, and BladeStorm are excellent epic talents for Melee attackers.

However, you may also like Repel Boarders, which has a possible attack when enemies get within range.
Cheap shot if an enemy flees or tries to move out of your range. Although this talent can backfire on you!
Flanking is a very interesting epic talent, although do not get flanking 2 as it does not work like it used to. Flanking is a very strategic epic talent that gives you a second hit chance if you have another melee person on the opposite side of the enemy you are attacking.

Quick Draw, Burst Fire, and Double tap are great epic talents for Ranged attackers.

Some like overwatch, which has a chance to fire when enemies get within range. Some like True Grit, as it returns fire when you are hit, since ranged attackers rarely miss. Return fire is not very practical, since most ranged weapon companions can not train dodge!

As for Old Scratch and Mormo, I will say this until I am blue in the face, but advanced mojo strike 2 and Mojo Echo 2 all the way. Would never change that, but then, these are my preferences and opinions!

Hope these ideas help.

Personally, I like Kobe Yojimbo with First strike, Riposte, and relentless 2!
Witchdoctors can also give a haste that gives first strike and riposte, so that would make a character like him setup with First Strike 2, Riposte 2, and Relentless 2! Talk about a 1 man army!

As for Kan Po, I like him with Riposte 2 and Relentless 2.

These are just my choices and preferences, we all have our own.

A lot depends on the class.

However, I tend to avoid the double up damage talents in favor of the "hit when they hit" or "hit when I miss" to help insure that I continually do damage to the enemy. Then means Vengence Strike, Second Chance, etc. First Strike is another good one, since with it you can defeat a weak enemy before he has a chance to strike.

Once you get a character with a lot of these epic talents, you will want them as your first mate, as they will often be attacking three, four, five times a round.