Although this thread is a bit dated, I'd like to add a few things to it.
I play both a level 59 necro and a 53 wizard as of the time of this writing. I can honestly say that both classes are great fun, have many options, and ca ndo well in groups or solo. However, since this thread is about the nuance of solo-ability of the two classes, I'll break it down into my usual list.
Necromancer - PROS
1. More "get out of jail free" cards - feign death line, harmshield line.
2. Can fear opponents - this can prevent them from casting on you.
3. They get a nice pet - only magicians and beastlords have better pets for their level.
4. Get the lich line - greatly adds to their ability to recover mana - wizards only get harvest, which is obsolete past 50. Also, necro's can pump up their party's mana (at the cost of their own).
5. Necro's can heal themselves using their lifetaps and the leech line.
6. Necro's can heal party members using spells like shadowbond (that whole line of spells, actually).
7. Necro's can debuff an enemy (though not as well as a shaman or an enchanter).
8. Necro's have the ability to buff the party as they debuff the enemy as well.
9. An entire family of spells (dozens) that have everything to do with destroying, controlling, charming, calming, summoning, detecting, and hiding from...the undead. Not even clerics and paladins can match a necromancers affinity for the dead. Wait, that didn't come out right.
Necro, CONS
1. Very limited ability to teleport around - gate, levant, succor, shadowstep - that's about it.
2. Faction issues, due to evil class / evil deity.
3. Takes longer to kill an individual monster compared to a wizard. This can present its own set of problems, especially in PvP.
Wizard, PROS
1. Ability to port around to many places, even send a person on while you stay behind (translocate).
2. The ability to kill an enemy quickly - as long as your spells are not resisted or interrupted (high DPS).
3. The ability to snare without causing damage to a mob - this can really help in groups where mobs are mezzed.
4. In general, wizards are more in demand for groups, due to #1 and #2, above.
The above represents my conclusions of the two classes after playing both off and on for the last several years, but I repeat that both classes are very entertaining to play.
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If you can't do something well, learn to enjoy doing it poorly.
My Rathe / Prexus characters:
Bigbronze Bloodyaxe, 62 Ogre Berserker
Verbeeg Bearfang, 62 Ogre Beastlord
Glabrezu Spiritcaller, 62 Ogre Shaman
Zirumkin Zenomorph, 62 Gnome Wizard
Korgulon Soulwraith, 76 Ogre Shadowknight <Shining Alliance>
Incarnadine Summoner, 65 Drakkin Magician
Bristlebane characters:
Zalkahriz Ebonscale, 64 Iksar Necromancer
Gnomorre Gniceguy, 55 Gnome Rogue
Whytfire Lonewolf, 55 Woodelf Ranger