My mage is a grade 3 initiate with Masking, extended masking, and shielding. Would you go for a level 4 initiate for centering, or spend those points on stunball(don't have any AoE spells yet) another spell and specializing in a couple skills. I'm trending towards the spells, but I really want centering.

If you go for the spells, seriously consider one of the indirect ones since not having to have LoS to everyone in the AoE can be a big bonus.

In the situation you described, I would go for the stun ball, other spells, and specializations. Stunball is extremely drain friendly and can be cast at high levels even without the benefits of centering....plus the AOE is amazing. Specializations can really help you summon a bigger spirit or have your spell be harder to resist.

Something to consider, possibly, would just be only buying the stunball spell for 5 karma, and then saving up for centering, it doesn't have to be an all or nothing situation where you either get the initiation or you spend all of your karma down to zero.

I say go for centering. At your new initiation level, that's 4 extra dice for drain from a free action. Too good to pass up, in my opinion. I assume your current spell list is competent, so you really just want some shiny toys - but 5 karma is roughly one session's worth of karma, so you should be able to get your spells one at a time after you initiate.

my spell list has been getting me by. What I want to fill out is a couple illusion spells, a couple more detects and a AoE spell both direct and indirect. I'm not as rounded as I'd like due to a player change. We had a second mage who decided he'd rather play a perception adept, and the spells he was covering I don't have. Thing is we have three technomances so I have not been that worried on the illusion side for tech security. and we've been conning, mundane disguising ourselves past physical security(2 secondary faces). But in fights, I've been a big gun just not able to handle multiple foes too well.

Current Spell List
Intoxicate
Levitate
Heal
Catalog
Analyze Truth
Increase Agility
Increase Reaction
Increase Reflexes
Physical Barrier
Power Bolt

What, no improved invisibility? O.o

isn't that why he said he wanted to fill out a few illusion spells?

Did not read anything like that. Probably my failure somehow.
Else, if you wanna be usefull, try and find out what the TM's and other Guys are mostly using.
If the TM's are doing stuff with their attributes, Raise Attribute Spell for that one would be good.

Unless you got a good astral combat skill with a weapon focus, you need to pick up manabolt or stunbolt, otherwise spirits will tear you apart in astral space. Otherwise I find influence, trid phantasm, and improved invisibility to be some of the most versitile and useful spells in the game.

Now that we are talking about "spending karma": if you really don´t know where to place it, give it to me. ^^