Imagine you're beginning a campaign, only instead of the base classes, you begin in a prestige class. You must meet the prerequisites as soon as possible (so your first few feats and skill points may be predetermined for you you). If it's a class that advances casting, pick the casting of a class that could qualify for the PrC.
What prestige class would you start as?
|Tiny Coffee Golem|
Mystic Theurge Wiz Cle. I got one up to level 25 the hard way (3.5 not even pf). Yes they are not optimized by MinMaxing standards, but when you have over 80 spells per day, I can guarantee you that you will never run out of stuff to do.
Even at lower levels he will never be subpar because he will never encounter the slow down in power the prestige class normally suffers because you are doing it from level one.
I think the multiclass spellcaster prestige classes would just wipe the floor with all the others. The Assasin is basically a killing focused rogue variant, while the theurge is basically a gestalt.
Such prestige classes wouldn't even exist if it weren't for the fact that multiclass spellcasters don't work in the slightest without them. Their flavour is identical to that of a multiclass character's.
I think if one were to do this, one would need to require characters to qualify normally for the eldritch knight, mystic theurge, arcane trickster and the like, or make it clear that you're supposed to play them and only them.
EDIT: How would you guys handle weapon and armour proficiency? GM assigns the proficiencies of whichever class seems most appropriate?
EDIT 2: Shouldn't this start at level 2? A lot of prestige classes have a pretty much dead or otherwise dull first level.