As my regular players are already aware I have decided to convert to the Pathfinder RPG with the advent of my next campaign.
The 3.5 / Pathfinder / 4th edition Debate is a useful one, but ultimately one which has to be decided on an individual baisis group by group, player by player.
My reasons for choosing pathfinder are my own. I don't disparage the other systems, if you find then enjoyable I would encourage you to go play them, but I find pathfinder to be more my cup of tea for my own games.
Comparing 3.5 to Pathfinder:
I like Pathfinder for many of the same reasons I like 3.5 but pathfinder solves many issues and potential issues with 3.5 that were frustrating for me.
Particularly among these: Save or Die spells, Polymorph.
I am very fond of the increase in power to base classes and races. I like that I can have an NPC with no prestige class levels now who feels customizable, and crunchy from a challenge perspective.
I am also impressed with Paizo's commitment to keep the system firmly within the realm of open game content.
Pathfinder vs 3.5 (adapted from a Paizo announcement)
1. Grappling, disarming, or bull rushing a monster no longer requires you to have a master's degree in combat rules with a minor in spatial mechanics.
2. Using a polymorph spell does not require 3 different FAQ documents, 4 bestiaries, and a mountain of house rules.
3. Clerics can actually cast their prepared spells instead of converting them into healing. Clerics can now channel energy to heal the party and turn undead.
4. Bards don't suck. Now they can make you die with laughter.
5. Monks don't suck. When they use flurry of blows they actually hit.
6. Paladins don't suck. Smite evil lasts until your target is dead.
7. Rangers don't suck. You really do not want to be a ranger's quarry.
8. Sorcerers don't suck. Bloodlines give you a host of cool powers and abilities.
9. There is now a reason to wear medium armor. With a good Dexterity score, you can get an AC of 19 by just wearing a breastplate.
10. Building the skill list of a rogue 5/barbarian 3/assassin 2 now only takes about 2 minutes.
11. Use Rope is gone. Climbing a wall requires only one skill check.
12. Spellcasters do not have to spend a bunch of ranks on Concentration (or any other skill) to be able to cast their spells in the middle of combat.
13. At high levels, a fighter can cause a character to become blinded and stunned with a critical hit.
14. At high levels, a paladin can cure a character that is blinded and stunned with a touch.
15. Curses, diseases, and poisons are now something that the players want to avoid contracting.
16. Putting together an encounter only requires you to add up the XP totals of the monsters you are using.
17. You do not have to wear a Christmas tree of magic items to be a successful adventurer. Monsters are designed with normal characters in mind.
18. Creating magic items now comes with the risk of making a cursed item if you are not well-prepared and careful.
19. You never, ever have to "de-level" your character.
20. With more healing and reusable abilities, the 15-minute adventuring day is a thing of the past.