>Can you guys comment on what spirits you prefer (and why).
I think that the best basic spirit is Spirit of man. He has the Innate Spell optional power (Improved invisibility, stun bolt, increase [attribute], increase reflexes are good spells for the spirit). If you can take a possession tradition you can also get a task spirit with Skill Optional power ( useful skills: demolitions, locksmith, first aid, armorer etc). So, one of the best tradition is Vodou, they get both before mentioned spirits. Drain is will+ cha, so an elf with Vodou tradition is a strong mage indeed.
If you face e.g. F10 spirit, it have typically 1-2 services and it's unbound. If you want to bind F10 spirit, you need 5000 money and >20 dice in your binding pool (magic+binding+focus+situational bonuses (specialization)) to success more than 50% surely. It is quite much. Bound F10 spirits are summoned by high elite mages and that's why they are rare enemies.
It is quite easy to banish unbound F10 spirit. In basic setup it's 12 v. 10 dices, and if you success to remove one service, the spirit is probably gone.