Main diff between Mage and Necro?
 

It seems like most people say Mage, Necro and Druid are the best class's to farm with. I know why Druids are good, and I am guessing Necro/Mage good because of pets but, whats is the difference between the two? What does one class offer that the other doesnt? Other then one is KOS and has a skeleton and the other can summon food and has a earth ele?

Necro has more mana regen and more efficient damage done per mana generally. Magicians get stronger pets (different strengths from different pets) and superior burst damage. Dots are horrible at agro, though, causing considerably more agro per damage done than nukes, making mages easier to play in most team settings.

Necros can snare kite, fear kite, root, FD, split, invis to undead, & mez. The mage solution to all those utilities is "let the pet tank it", which it does better than the necro.

Mage summoned items are neat, but nowhere near the scale of necro utility.

Necro faction is overstated. Most necros can go anywhere a mage can with the exception of felwithe, kelethin, and kaladim (edit: and I'd have to check that, having originally been an iksar myself). That, and some mages can't go to paineel or neriak, which are usually ok for a necro.

agrees with previous post. I play a mage, and would love to have some of the abilities of a necro..our pets are great..the 29 fire pet for example gets a 27-29 ish DS....the air pet stuns and interrupts casters well.

for me the best things that necros have that mages dont is the mana regen and FD.

both are fun to play.

Biggest difference not covered by two above posters is that necro actually gets better as expansions unfold, whereas mage pet dps and nukes take a nosedive.

I was always impressed with the mage epic pet in older content.

Nose dive is a bit excessive. Mage DPS is fine in kunark and velious, its just the mobs last long enough for DoTs to actually work so Necros start getting better.

Mages have no utility, but they rock.
Necros have LOTS of utility, and also rock.

Mages can solo anything that doesn't summon.
Necros can solo anything that doesn't summon.

Mages can summon food/water.
Necros can FD.

Two mages can kill anything.
Two necros can kill anything.... that doesn't summon.

Fixed, why would i care about things that summon my PET? ;) Only top 1 of the hate list will be summoned, wich is 99,999% of the time my pet, unless i overnuke, and then i deserve the spank ...

It's very difficult / nearly impossible to chain pet on summoning mobs, unless there's > 1 magician.

Well, because NPCs won't summon pets, but instead the highest aggro PC. However I'm not high enough to be killing mobs that summon here, so someone else will have to tell you if thats the case on p99.