My two bettas, Cartman and Klaus, are amazing me with their personalities. I had a betta, Gil, a few years back, and he was a sweet, laid-back little guy who had a nice, long lifespan. I figured all bettas were like him, but I'm quickly learning they have very distinctive personalities.
Cartman is actually a lot like Gil. He's calm and curious and just hangs out or explores his habitat (6 gallon Edge) at a leisurely pace. He enjoys it if I put something new in there to explore. He makes me feel bad that Gil lived his whole life in a 1.5 gallon habitat; I believed the BS about small bowls being better, but seeing how Cartman likes to swim around every inch of space makes me realize how wrong that is.
I bought suicidal Kenny at the same time as Cartman, but in the brief time I had him, he was such a happy, energetic little guy. He was constantly in motion and loved to watch me from his 2.6 gallon Spec, which is in my workspace. He realized almost instantly what feeding was all about and was the friendliest little guy. I'm still upset about his disappearance.
Klaus replaced Kenny, but even though their coloring is somewhat alike, Klaus's personality is totally different. He's a flighty, aggressive betta who flares at pretty much anything (or nothing). Kenny wouldn't even flare at a mirror. He was leery of me at first, but now he's decided I'm harmless. He patrols his tank constantly and has already dispatched two or three ghost shrimp (Cartman leaves his alone). He's an absolute pig at mealtimes and attacks his food viciously, even though he's well fed. He's quite the character.
That's three different bettas and three different personalities. This makes me even sadder to see how they're treated in stores. People act like they're not living things with feelings, but they're really packed with personality.