This is one of the classic EQ arguements.....
First off, leveling your Wizzard is not as hard as some folks make it out to be. I never really had any trouble finding small groups (PC, MSERU, GD,PAW) up to level 34. Then I quadded in various zones to mid 50s. When not quadding, I would go LFG in various zones (or LDoN) and, if nothing came up quickly, I would start my own groups. Being in a guild, I usually had one or two others to start a group with. The toughest time was from 60-65. I tend to play a lot of LDoNs, and everyone forming a 60's group wants as many 65s as possible to get the highest level dungeon. Those types of groups are more willing to go a bit lower for a healer, slower, or tank, but DPS classes tend to be more plentiful and the level 65s get the groups.
I can say that playing style does play a big role in what class you play...
If you are not in a guild and tend to solo alot... MAGE
If you are in a guild and/or like to group... EITHER
If you like a character that never needs to look for a ride or run somewhere.... WIZZY
I would also like to say that as player whoes main is a Wizzard, I always have lots of fun when grouped with a Mage! Massive DPS and you both take advantage of the pet.
Finally, whatever class you choose, you will usually have no trouble finding a group if you learn to play your class well. Both Wizzies and Mages have good resources ( www.graffe.com for Wizzies ) on the web. I also learned a lot by picking the brains of other wizzards....