I'm 17, i started taking martial arts at the age of 10, because I was tiny and wanted to get bigger, and etc. I go to a gym where they offer pretty much everything you can take. I started with Karate and Brazilian Jiu Jitsu, then years later still while taking karate, I took muay thai and boxing at the same time, to vary the style.
To answer your question, I would take both a stand up and a ground-fighting martial art. For the ground-fight, take Jiu Jitsu, it's your best option and the most effective. But of course if you have 5 or 6 guys on you, and you don't feel like running, or you can't because they're surrounding you, submitting each guy will not work, i don't recommend tryin it, unless you wanna get killed.
For standup, I would recommend basically any martial art. Muay thai is very effective, karate is good (not to fight your guys with a form technique, but to kick them instead). Boxing is ok, but knowing how to kick is VERY important (because of reach).
Now, onto the "exposed groin." Your groin is exposed anyway. Plus, why would you kick him on the head. I'd kick his leg if the opportunity came up. Break his damn knee or tendon. Then when he's down knee him on the chin or something.
Bottom line, Standup AND ground..
hope this helped
Close to 8 years of Karate/BJJ/Muay Thai/Boxing