Twenty years here, and counting!
For me, you need the playfulness. I'm a huge teaser, but not in a mean way. She's a bit of a "force of nature", you know, tends to fill up a room. I can keep her grounded and away from spinning out of control by using humour. It's a good defense mechanism too...
She's definitely my best friend, and I get grouchy when I don't get to talk to her and let her talk to me...like when we're on opposite schedules/shifts.
The physical chemistry is important, but it changes with time...not to go into any boring/gross details, but that part becomes less about actual body parts and more about your most important sex organ...your brain...betcha thought I was gonna say something different...😉
Best feeling: the feeling of peace when you're together, no matter what is occuring...as long as you're together, nothing is insurmountable, and all will be well. That's the best chemistry of all!