Humans: Two feats right off the bat, allowing for precise shot and point blank shot at first level. No other race can expect such reasonable use of a crossbow inbetween spells at low levels. Small races in general get hit bonus and ac bonus from their size, which can come in handy with using ray spells or missile weapons. Gnomes get a +1 to DC of illusion spells. Ultimately in the long run no one will be better than the gnome with phantasmal killer. Elves have longswords and longbows, if that's your thing, and a high dexterity useful for AC and hit rolls. Dwarves have the con bonuses if for some reason your wizard is getting hit. I end up torn between the Gnome and the Human wizard.
Only humans, half elves, and elves can have wizard as a favored class, so if you are going to multiclass, there is that to consider.
If dwarves got the +4 to resist trip attempts that would be useful. In vanilla I believe they get improved trip for free at first level Co8 thought this was overpowered and took it away. The +2 Dex for Elves is also good for +1 initiative.
One thing to consider about small races (except dwarves) is that they can't wield quarterstaves, and thus will be unable to cast using crafted or other in-game magical staves (e.g. the Fire and Ice staves from Verbo).