Bonnie never thought too much about her sexuality.
It never mattered to her what was on the outside, it was always about how that person made her feel. She guessed it was a witch thing, even when she wasn't aware of being a witch. Some people just had good hearts, and/or an intriguing aura that made Bonnie want to be around them.
Like Tyler. Even though on the surface he seemed like just your typical jock filled to the brim with excess testosterone, Bonnie also knew he took every dig, every drunken insult his father lobbed at him to heart. For every time he passed off his feelings with a smirk and joke, there were just as many times that he snuck off to Bonnie's home to vent and sometimes cry on her shoulder.
And Rebekah. The blonde original presented to the world as someone not to be trifled with. On the surface, she was cool, calm, and collected while hidden underneath there was a girl forever stuck in that young adult phase who desperately wanted someone to see her, love her, choose her.
Bonnie would never say it, lest she be subjected to a screaming earful, but Rebekah and Caroline were more alike than they realized.
Both Tyler and Rebekah were scared kids just trying to find their way in the world, with a tough outer shell in order to protect themselves. Bonnie could understand and see the beauty in that.
Not to mention the beauty they presented on the outside. Tyler was all smooth muscles and tanned skin that Bonnie sometimes had to physically restrain herself from reaching out to touch. Not that he would have minded, they had hooked up a few times before he got with Caroline. After his relationship with her imploded, he'd made it clear that he wouldn't mind resuming their casual encounters. The witch in her pulsed at that thought, and Bonnie very nearly gave in to her curiosity. But of course something was threatening them once more, and what she personally wanted was put on hold for the greater good. By the time the dust settled, Tyler was gone, handling pack stuff, but promising to come back eventually.
Rebekah was on the opposite end of the spectrum; tall, thin, and pale skin with legs that seemed to go on for miles. She's not sure why Caroline never had the same effect on her, seeing as they were pretty similar looking (again, never telling her BFF that). She didn't get to interact much with the original, most of their exposure to each other was in their shared physics class. Bonnie had been known to space out just staring at the back of Rebekah's impeccably coifed head and wonder what she would feel like in her arms. What she would sound like if Bonnie gave in to her desire...what she would taste like on Bonnie's tongue. The only acknowledgement Rebekah ever gave was that devilish smile she shot Bonnie while Damon hung suspended from the ceiling: "see you in Physics class".
She admittedly got a kick out of Mary Louise's feelings of jealousy and made sure egg on the heretic whenever she could. Yes she was flirting with Nora, but upon further reflection she wasn't sure if she was attracted to her, or because she was so similar to another dark haired, short tempered, siphoner that happened to be a Gemini. She recalled a very pleasant dream which started out with just Nora, but shifted to include Kai that left Bonnie flushed and aching with arousal upon awakening.
So no, Bonnie doesn't necessarily have a type, the only requirement seems to be the ability to make her want.