Okay, first, get rid of your 4th Edition books. I might even suggest burning them, unless you feel compelled to hide them away from where they may never be seen again and not destroy them.
Now, go out and get the 3.5 core set.
...Anyway, my favorite? No clue to be honest, I like a hell of a lot of them. With my group, I'm the DM. I have been for... well... quite a while now. So I don't get to play often. Whenever I do, it tends to be different. Most recently? I played a gnome cleric for a spoof. Once per day his strength jumps from 13 to 40 for a few rounds as a free action, in which he will most likely murder everyone nearby, considering he's lvl 11. Well, maybe not, that's generic, and I have many stronger things. Eh, it's what we get for fun.
If I may make a note, perhaps my favorites are my big three. I made a set of evil characters which recur through my stories. Teclis, the slaughterer. Black Asis. Orthoz... heh, the bogeyman.
...Looks like this'll be a long one.
Hmm, okay, wizard or sorcerer, you become horrible the moment you take sudden metamagic feats. 'Complete Arcane' I believe. You can suddenly do a maximized, empowered, quickened version of one of your spells. I suggest a ray spell, then add a twin spell or a split ray metamagic rod to the mix. At lvl 11, you opponent is looking down the barrel of 396 damage. With no save, and no actions spent yet. It can get worse than that even, very very easily.
Bard? Well, I've never played this bard in particular, just had him used in my campaign. At lvl 10, he gave every part member 8d10 sonic damage to each of their attacks. That was one song. With his four lvl 10 companions, they took on a CR 22 encounter and won, even if only just. That bard used 'Races of the dragon,' as well as 'Celestial choir' from 'Exalted deeds.' ...I had to get him to change to a different character. That one was unholy on a whole different level. The painful bit? That character could get much more powerful very quickly.
Cleric is impossibly easy to bastardize. If you go through 'spell compendium' you gain access to spells which should be three levels lower, ...and a 5th lvl true resurrection that only costs 1000gp. And it's a standard action. However, the great pain comes from either of these two feats. 'Divine Metamagic' or 'Divine spell power.' Both are from 'Complete Divine.' Look them up. Look on in horror...
There are so many ways to bastardize a rogue. However, all you need is one. 'Staggering strike.' If I recall, that feat is from 'Complete Scoundrel.' When you sneak something, the have to make a fortitude save or do nothing next round. The DC is equal to the damage dealt. So, often 50+. Goodbye CR 27 great wyrm gold dragon.
Rangers are actually a little trickier. However, you can have a stupid amount of fun with them. 'Cragtop archer'. Prestige class. 'Races of stone.' You can shoot things, with no penalties to attack bonus, at about 1650 feet. ...At a low level. Even the very fast dragon will be shot at for five rounds or more before he even gets there.
Barbarian. Oh why... The unholy king of easy bastardization. First off, a class variant from 'Complete champion' gives you pounce on the first level. For those who don't know, that means a full attack on the charge. It's one of the nastiest abilities out there, especially as you go up in levels. However, it has always been feats which create the worst things. Look these up. 'Karmic Strike' 'Robilar's Gambit' You take both of those, and for a sacrifice of AC, which the barbarian doesn't have in the first place (so no loss what so ever) every time someone attack you, you attack them back. Immediately. TWICE! One character in my campaign was fond of running zig-zags through enemies, provoking as many attacks of opportunity as possible just so he got 12 attacks on the enemy at lvl 6. Now, he'd obtained damage reduction, so none of these attacks of opportunity hurt him. Do I smell busted character?
Perhaps I shouldn't continue far. But I'll make a note or two. First. The Druid with four pets. The monk whose fists hit for 1216d6 damage. Fighters are an extension of barbarians, with extra feats to do bad things with.
Do you remember the three characters I spoke about earlier?
1. Teclis is a rogue 14, scout 1. Human. He deals 22d6 points of sneak/skirmish damage with each hit as part of a sneak attack. ...Which he always gets, even against constructs or undead. His hide modifier is +60something. Therefore the slaughterer.
2. Asis is a wizard 3, sorcerer 2, ultimate magus 10. Human. He can cast a chained dominate spell (chained meaning it'll hit an entire group). The DC is over 60. He owns epic dragons at lvl 15.
3. The bogeyman. 'Cause he'll never see combat. Orthoz is by far and above the worst. He is my prize creation. The monster that will never fight a party, cause he'll kill them all. As well as whatever demigods they happen to be hiding behind. I won't mention much, apart from the fact he's a killoren. An off race from 'Races of the Wild' that does little more than change his type. It was mostly for flavor. 'Jack of all trades' (which means you have a half rank in every skill) went into it. Again, he's level 15, but he can make a DC 100 bluff check. ...Or knowledge(Masonry) check. ...Or Craft(tissues) check. Or DC1000. Or DC10000. I can't remember my maths, but it may have been over 100,000 too. Not all good for combat, you ask? Well, he gains roughly 400hp each round. Excess go into temporary hit points. His attack bonus is in the hundreds, so is his damage. This is a legal 15th lvl character. ...The scary part? I could make him above lvl 20. He could be a mage. For those versed in the epic levels and epic spellcasting, he can make a DC50000 spellcraft check. Wrath of God? Bah. He can cast spells over 100x in power. Or could, but that shall never exist.
Oh, and for those not versed in it, wrath of god is an epic spell that deal 305d6 points of damage. You have to make a skill check of over 300 to cast it. It's supposed to kill anything... And Orthoz can survive it, and several hundreds of it's brethren.
...You know what? I've digressed. Through all of this, I haven't mentioned my favorites. Whether alignment, class or other. Perhaps because I like them all. Anyway, I've wasted a humongous amount of time writing this. And I wonder what was the point? Who knows. Perhaps I felt like getting in on the rant. I'd love replies to this though, I have to big a hobby in D&D... Heh.
So, how was that for a first post? HAH!