It's not really accurate to say Voodoo is the best. Voodoo is the best of the Charisma traditions, but that's by default. There are good reasons to be a Charisma possession mage, but that's hardly the only useful type of possession mage.
Generally speaking, each type has their advantages:
Charisma: being an Elf, more bound spirits (very good with Possession, since low-force Bound possession spirits are still plenty dangerous).
Intuition: Other types of mages can't afford to dumpstat intuition, unless they are willing to suck at perception, assensing, and combat (since it affects Initiative), but you can be an Intuition mage and have low Logic and Charisma (probably 2 in each so you don't get GM aggro, and it's good to have 2 focus slots). Because of how Possession overwrites your mental stats, this is a good plan if you don't want to self-possess, and instead want to stick your spirits into Homonculi or corpses.
Logic: Being cybered. This one is actually potentially very, very broken, because spirits actually overwrite your magic when possessing you, and they still overwrite your Magic when you have Channeling. So you can lose Magic to cyberware that gives you buckets of drain dice and passive defenses (eg, armored cyberlimbs), and then get it back by having a big spirit possess you. Even if your GM houserules that away, it's still not a bad way to work.
Voodoo is the only Charisma possession tradition and already has great spirit selection anyways.
Likewise, Qabbala is the only Logic possession tradition. They have OK spirit selection. Task is there, which is key, because task is really great.
Intuition is where you actually have a choice.
Psionic is incredibly terrible because they have huge, huge random drawbacks - no mentor spirit (sucks), no enchanting vessels (double sucks), and vaguely worded things about how you can't learn most spells (maybe sucks). Don't do it unless you intentionally want to make a weaker possession mage. I also really hate the flavor; these guys are basically the equivalent of the Flat Earth Society.
IMO Hedge Witchcraft is the best. The reason for this is that Task is far and away the best of the "utility" type spirits, and any spirit type with Element Aura and Engulf is enormously dangerous in melee (A fire spirit in a Plasteel homonculus punches people for F+11/-half, which is crazy). Between Water, Air, and Task, they have most of the useful powers, Air is perfectly good at fighting, Earth is mostly worthless, and Plant has the niche Silence ability, and the very good Regeneration great form which allows for hilarious regenerating truck antics. No Guidance means no free Divination, and no Guardian locks out the weapon-based combat route, but really, Engulf+Element Aura is plenty dangerous.
Rastafarian is defensible. They get Guidance, which is neat, and Man, which opens up a lot of useful tricks. Man spirits are really good for Materialization, but only meh for Possession - the reason is that they will just have Force in mental attributes and skills, but can easily have crazy huge physical attributes because of how Possession works, so relying on physical combat generally works better for spirits. That said, you can still do neat things with them. The real issue is that Rastafarians don't have Task, and Task is really good and IMO worth more than Man and Guidance put together.
Egyptian is just less good spirit selection than Rastafarian. Fire/Earth/Air for Man/Beast/Plant is not at all a good trade.
