I agree that VF4 is better than Tekken 4, but on the subject of Tekken, here's my picks :
1) Paul. Power, speed, reversals, excellent low attacks. Paul's high damage attacks and decent juggle ability make him tough to put away. When it looks like Paul is getting blown out his Phoenix Smasher (stone breaker, power punch, or whatever you want to call it) deals big time damage and floors your opponent. Paul's ability to float an enemy and keep an enemy down makes him even more dangerous. Paul's counter is a nice addition. His only weakness is when he whiffs, but most good Paul players won't do that. My personal #1
2) Nina. Toned down a bit in this installment, but still dangerous. Her juggles are fast and dangerous, she can easily keep an opponent down, has a chain throw that hits off the run, and a couple of decent standing chain throws (although anyone can escape them now, they've been around forever). Throw in a sweet counter that can even stop Yoshi's sword and you're all set. Her speed makes her good with keep away's and poking strategy, while her Spinning low to high kick is a great juggle that always launches on a counter.
3) Heihachi. Three old school Tekken characters on my list, but hey I call them as I see them. Heihachi seems to be hitting harder with age, and his Demon Sweeps to Uppercut combo is brutal up against a wall. His juggles are old-school but devastating. He only needs to get you once and you're in trouble. Not much has changed with the old man since Tekken 2 really, but he still hits like a truck, can keep you in the air for a long time, and crush you on the ground.
Thats my personal top three, but I must concede that any character can beat any other character in the hands of a good player. You can also make a strong argument for Law on this list, but these are my personal favorites.