I have zero XP with 3pp material in PF, but I'll do my best.
Anything in particular that you are aiming to do, like specialty? Grapple, high dpr, etc.
PF almost encourages multiclass mundanes, being very front heavy. Archetypes are pseudo-PrCs. The limited PrC selection only recently opened up with these two feat, adding a handful of casting PrCs to the ranks of usable ones.
Favored Prestige Class
You have come to favor a certain prestige class, either
because you are particularly devoted to the class’s cause,
have trained more than most others have for that specific
role, or have simply been destined to excel in the prestige
class all along. Regardless of the reason, levels gained in
your favored prestige class grant additional benefits in a
way similar to those you gain for taking levels in your base
favored class.
Benefit: Choose one prestige class and one skill that is a
class skill for that prestige class. Whenever you gain a level
in that prestige class, you receive +1 hit point or +1 skill
rank. You gain a +2 bonus on checks using the skill you
chose from that prestige class’s class skills. If you have 10
or more ranks in one of these skills, the bonus increases to
+4 for that skill. This bonus stacks with the bonus granted
by Skill Focus, but does not stack with a bonus granted
by any other feat (such as Magical Aptitude or Persuasive).
The choice of favored prestige class cannot be changed
once you make it. Levels in a favored prestige class are
not the same as levels in a regular favored class, and as
such levels in a favored prestige class can never be used to
qualify or gain favored class options like those introduced
in Pathfinder RPG Advanced Player’s Guide. You can have
only one favored prestige class, but can still have a favored
base class as well.
You can select this feat before you gain levels in your
chosen favored prestige class, but the benefits of the feat
do not apply until you actually gain at least 1 level in that
prestige class.
Normal: Prestige classes cannot be a favored class, and
cannot benefit from the additional hit point or skill rank
afforded to those who take levels in a favored class.
Prestigious Spellcaster
The transition into a spellcasting prestige class is less
difficult for you, and because of this, you gain 1 additional
effective spellcaster level from your prestige class levels.
Prerequisite: Favored Prestige Class with selected
prestige class.
Benefit: The first time you gain a level in your favored
prestige class and the spells per day class feature does
not grant an increase in effective level for the purpose of
casting spells, you gain new spells per day as if the prestige
class did grant +1 level of spellcasting for that level. This
effect is retroactive if you gain this feat at a level beyond the
point where your favored prestige class would normally
have not advanced your spellcasting.
The Prestigious Spellcaster feat does not have any
effect if your favored prestige class does not have the
spells per day class feature, or if it does have the spells
per day class feature but already grants a level increase for
every level of the prestige class (as do the arcane trickster
and loremaster prestige classes).
Special: You can select the Prestigious Spellcaster
feat multiple times. Each time you select the Prestigious
Spellcaster feat, your effective caster level increases by 1.
However, regardless of the number of times you choose
this feat, the total increase to your effective caster level
cannot exceed your actual prestige class level.
This feat also applies to prestige classes that grant
extracts per day instead of spells per day.
