I am curious to hear the answers for this as well. Perhaps it's found elsewhere in these forums, but without necro'ing a forum (yes, that was said tongue in cheek) I wouldn't mind seeing some replies here. My first alt is a necro and I've not found a merc I'm entirely happy with.
My Necro's #1 choice for a Merc is: None, they get in the way of my Necro and only slow them down or casue problems. After that I usually run with a Drige Merc so I can run faster in Dungeons. I might try the new COE Trouby Merc, but last time I tried the Trouby he stunk. I often run with Inquisitors for the sole purpose of casting cure spells. Necro's are tanks, healers and DPS all rolled into a single toon. I've tried the Assassin Merc and that wasn't too bad if you consider it nothing more than an extra DOT.
Well for leveling all you really need is tainted heals and your tank pet but if you don't have enough AA for that I'd suggest using the shadowknight merc with your mage pet. Her death march and harm touch makes your job a lot easier. At max level the only merc I use once in a while is the inquisitor with myself acting as the tank and my mage pet for additional dps.
I have Matri. She is like the Tank pet on steroids. Huge DPS, fast and is always welcome as a front liner with the melee classes. I will usually take the Mage pet when she is out and set Matri to follow/assist the MT. Unless the group wipes, she has incredible staying power. Only real downside is the long 5 minute wait if she does go down. Luckily my usual MT is a Pally with Perrin so he is likely waiting too. Before Epic mercs, I used a SK merc with good results. I have also experimented with that dwarf (Templar?). My buddy nicknamed it Foolish with very good reason. I think I have also used a Guardian, but since I don't remember it's likely that I was not impressed with it.
I just got Kenny and I'm really liking it. He's a good healer (most of the time) and curer, and can dps along with me.
After re-reading some of the responses I have to agree with Koleg a lot... actually... the best merc is... someone else's. Find a tank and he'll have a healer merc, and then you tag along and do what you do best without needing one.
