Can someone tell me why I'd rather one over the other?
I'd really like to hear both sides, figure what improved, what got clunkier in Pathfinder.
I can't tell you what is "improved" or what they did "poorly", because that would be a matter of individual taste. However, I can show some differences. I don't have this stuff memorized, so you Pathfinder fanboys don't jump down my throat if I make a mistake or I don't cover your favorite change. Feel free to add to what I'm saying here.
Races--slightly tweaked where pretty much all the races have a net +2 modifier to the ability scores. With the exception to humans and half-elves, the other races, get +2 to two abilities and -2 to one ability whereas humans and h/e get +2 to any ability of their choice. Other stuff too in the races, but nothing earthshaking.
Classes--some got tweaked, others got major revisions, but essentially it would seem that the classes have more abilities and powers. HD are more consistent to BAB. If you have a good BAB, you get a d10, okay BAB d8, poor BAB d6. Barbarians are the exception with d12.
My personal favorites is the treatment of cleric to channel positive/negative energy and sorcerers with their bloodlines in which they get certain abilities depending upon which bloodline they have for their character.
Feats--changes to some feats like power attack and cleave. For cleave, instead of getting an extra attack on an adjacent foe after you drop a baddie, you get an extra attack on a different foe should the first attack hit.
Skills--fewer. Example: Tumble, Balance, and Jump is now Acrobatics. Hide and Move Silently is now Stealth. The ranking system is different.
Rules--some examples is they removed XP costs in casting spells, they have a Combat Manuever Bonus for resolving Grapple and such, and turning undead is different in which the cleric can channel positive energy as a burst that deals damage and requires a Will save on the undead to flee from combat.
Again, I can't really say this is an improvement or a step in the wrong direction as everyone has different tastes. All my players downloaded the Beta which is free from Paizo, so you check it out.
My gaming group is enjoying Pathfinder ourselves and we haven't run into a major issues. It feels and pretty much plays like 3.x for us.