I'd look into either a pocket-type holster or maybe a sneaky pete. Back pocket of cycling jersey or jacket and you're good to go. Just make sure you maintain your gun's finish. Use common sense and be safe out there.
Well, I guess you might wound a couple with a little pocket .380. One might even bleed to death in a hour. Unless they were armed though, you'll be needing a good attorney. If they're carrying a real gun, (9mm +, 357, even a 38) though, a mortician will be more useful to you. As far as the efficacy of pepper spray, it's very effective. Five years ago on my bike I used a big fogger can on four guys intent on relieving me of my wallet. One good fog was enough to convince them to leave me alone. I've used it on a couple of dogs as well. Don't get me wrong, a firearm has its place, (I own several) but you need to know when and where it can be useful.
Recommendation: sub-compact SA or Glock 9mm, small of the back holster, along with the pepper spray fogger. If I had to pick only one, I'd carry the fogger.