If you are sticking with Tekken 6, the competitive meta eventually settled into these tiers after all balance patches were applied: Who was the BEST in Tekken 6? #shorts
If you are revisiting the original Tekken 6 (2009), version 1.03 is the "better" version because it is the required for online play on modern platforms.
In any fighting game, balance is a moving target. Tekken 6 introduced the "Rage" system—a mechanic that boosts a character's damage output when their health drops below a certain threshold. While the system was praised for creating tense, cinematic comebacks, initial damage scaling on certain characters was arguably overtuned.
Installing the update takes 90 seconds. Look for "Tekken 6 - Update 1.03 PKG" or check your PSN history if you bought it digitally.