Regarding fights going to the ground, I've been in 22 street fights, and about 1/3 of them went to the ground. I fought a majority of them with just a basic training in strikes and most of them were fought standing up. My longest stand-up fight lasted about 20 minutes against a guy who was a letterman wrestler in school. He didn't even try to take me to the ground, for some reason. My longest ground fight lasted about 25 mins with me against another wrestler, with me being on the bottom for about 22 of those minutes. That was when I was 19, back in '89. Back then, everyone trained in primarily striking, me included. I had no groundfighting knowledge whatsoever. I took a pretty good beating that day. But out of those 22 fights, every one was different, none resembled another. Some took place in snow, some on gravel, grass, pavement, some inside. Some took place in daytime, others in the dark. Some were fast-paced, some were slow. Some ended quickly, others dragged on. I was angered in some, scared to death in others. Some I took a serious beating, others I didn't have a scratch. I've suffered black eyes, broken nose 3 times, loose teeth, stitches, and overall bruised face and cut/puffed lip(s).
After I began studying muay thai & jujitsu, I've had one fight since then in, '99. The jujitsu worked great, with the fight lasting with only one punch swung, and me taking the guy to the ground. It was over in under 2 mins.
If I were to tell someone what to study, my answer would have to be to study it all. You simply don't know what the circumstances are going to be in the event of a physical altercation.
NHB events have shown us that a good groundfighter will likely defeat a stand up striker. Remember, though, that the majority of those on the street aren't versed in anything. Keep in mind, though, that even though someone isn't formally trained in a specific fighting style, doesn't mean they aren't going to know how to fight. I've seen, more than once, a very skilled karate practitioner get his ass whupped by an experienced street fighter with no formal self-defense training. I've also seen many practitioners of stand up striking (boxing, karate, tae kwon do) beat the crap out of others who thought they could fight.
No matter what you choose to study, you'll have an edge over those who have no ambition/drive into putting the effort into studying anything at all.