But thou shall not lose caster level is a very good mandate, althought that is all very good, i still think one more spell levels is better, especially at lower levels, when those level 3 spells can make all the difference in battle.
Indeed, while losing only one or two caster levels can still result in a good character, you must lose none at all in order to be GOD (one exception is
maybe Ultimate Magus, depending on how you build it, and the other is War Weaver). GOD does not encompass all effective spellcasters using the Wizard spell list, it encompasses a very specific subset of Wizards that are the best of the best at controlling the game.
For example, these are not GOD PrC's.
IotSV: It requires two crap feats to enter and simply doesn't pay off in the end. Half the veils are crap and all of them allow saving throws. The one truly abusable class feature is Kaleidoscopic Doom which is only really good if the target as at least 5 spell effects on it and then you must dispel them all, at which point the creature takes 140 points of various energy damages and must make two fortitude saves or be killed/petrified, but it's still a targeted effect that only works once per day. Compared to the other stuff you can do with your levels, this is crap.
Malconvoker: It loses a CL and goes against the principles of GOD: you're taking a direct involvement in combat as opposed to supporting allies and crippling enemies. GOD typically has better things to do than to clutter up the battlefield with a bunch of fiendish animals, and even if he doesn't he doesn't need Malconvoker levels to do it.
Wild Mage: Stop pushing Practiced Spellcaster/Wild Mage already. You net an average of 1 CL when you do that. ONE, not 1d6! Furthermore, Wild Mage requires the craptacular Magical Aptitude and does not compensate for it's loss. In other words, Wild Mage is absolutely NOT GOD.
Also, some good stuff...
Archmage: Costs 3 crappy feats, you say? Alright, then, lets see how it compensates:
Arcane Reach: Reach Spell without the adjustment.
Mastery of Elements: Energy Substitution x5 that you can apply on-the-fly.
Mastery of Shaping: Extraordinary Spell Aim without the skill check.
Reach Spell is one of those things that you either never use or always use. With Archmage you can use it some of the time and be really helped out by it. Energy Substitution sucks because it's 1 energy type and you still have to prepare it beforehand, the Archmage ability faces no such restrictions. Extraordinary Spell Aim is a staple for damn near every wizard build, but Archmages get a better version for free. Beyond that, you get two Archmage abilities for free. I know most people don't like Arcane Fire, but for FS Diviners (useful because you only lose 2 schools for all those spell slots), you can nab it and have some offensive punch. If you're not a FS Diviner, there's still Spell-Like Ability (Spell Power is crap IMO, 1CL isn't worth a 5th-level slot).
Mage of the Arcane Order: Spellpool is awesome, and while it requires a crappy feat to enter you're compensated at 2nd level.
Spellguard of Silverymoon: The only thing holding this PrC back is the Obligation. If you're in a campaign that takes place in the Silver Marches then you can almost certainly work with your GM to get the Obligation circumvented. If you're not playing in FR then you can still likely get the Obligation circumvented since you're also not going to benefit from any of the other first-level stuff. It requires Combat Casting, which sucks, but you're compensated at 2nd and get a free feat at 4th. Further, the requirement is shared with Abjurant Champion which can significantly bolster your AC and give you alternative spell uses if you care about such things. The big draw here is Selective Spell which is about on-par in terms of effectiveness with Extraordinary Spell Aim.
