My 2 cents...
Unless you're reasonably sure there won't be outside interference, stay on your feet. I have several years of wrestling experience and a few more of coaching it (on the mat, not sitting in a chair), so I'm not uncomfortable with it.
On the ground, you're a sitting duck. You're open to a bottle in the back of the head in the mount, a kick in the face in the guard, etc. Obviously you're open to attacks from others while standing, but you're in a far better situation to get away. Engaging in a jujitsu match in the bar, outside the bar or anywhere else in public should be a last resort. A single intruder in your home, in the cage, competition, one on one in a parking lot is a different matter.
And please, let's not get into a semantic debate about self defense vs fighting. If you're attacked and have no other options, it's self defense; call it whatever else you want.
With a faster opponent, it's all about getting off the line of attack, using and creating angles. Ducking, slipping, "bobbing and weaving," etc. Stand toe to toe with them, and you're asking for trouble. This is pretty much universally true though.
Use angles, weather the storm, and create openings. Don't wait for them to stop to counter, because you won't get the chance to. If the punch is half way there, it's usually already too late to move and counter effectively.