Depends on the situation really. I almost always prefer to stay on my feet, mostly so I can access my firearm or run the hell away (there have been exceptions in my past where I intentionally took a fight to the ground), but I've found that the chaotic nature of a fight means that what I want usually doesn't matter. If I'm going up against a better wrestler, I'm probably going to end up on the ground. If it's a crowded area, I'll probably end up clinched and might end up on the ground simply because there's no space to maneuver.
When I was working security at parties for my fraternity, I took most of the rowdy drunks down to tie them up and stop them from hitting me or going for something in their pockets. Worked well when I had other people to cover my back and keep others from putting boots to my head. Never had anybody actually try to stomp me, whether that was because no one wanted to or they saw the other Pikes standing around I don't know.
One time I got into with an gf's ex. He was a good boxer, or thought he was at least, decided he was gonna whip my A** to show how bad he was in front of his ex. Rather than stand and punch and kick with someone who was good in that area (I honestly thought I was a better boxer than him, I KNOW he had zero kicks and his clinch work was mostly hug and hold for the ref to break them up, so I was pretty sure I could take him without much problem standing), I took him down into a realm he knew nothing about, mounted him and pounded him senseless without taking a single punch myself.
Again, i had friends nearby to keep others from putting boots to my head while on the ground. None of them even got into pushing matches with others around, so not sure how much danger I would've been in from others had my friends not been there.
Hope for the best, expect the worst and always have backup plans and escape strategies.

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