I asked this same question a few weeks ago after reading the high times article regarding this subject and still was confused. While all the answers from other members helped, the only way to truly find out is to smoke the different types.
Just the other day I had my first encounter with indica. While I was anticipating getting blazed as it was high grade weed, I didn't. Instead of my surroundings becoming confusing, my vision being distorted slightly, my mouth being dry, my heart beating fast, and that "whoa" feeling I was accustomed to getting, I was FULLY aware of my surroundings, and instead of my mind becoming cloudy, it got extremely clear. Instead of feeling BLAZED, or high, I felt "stoned". My body didn't twitch like it does with what I was used to. Instead, my body felt extremely heavy, relaxed, and VERY comfortable. I was more social, and enlightened with everything.
Because of what people described indica as, I determined that this was indica. I'm not that big of a fan of it. While it makes your BODY feel nice, your mind doesn't really get affected. The other weed I've had was either sativa, or a hybrid of sativa and indica. That made me have the good mental effects along with some physical effects.
While the indica I've been smoking makes my body feel good and nice, it kind of is a disapointment if you go into it expecting to get baked for a few hours. I'd chose the mid-grade that I get, which I presume is a indica/sativa hybrid over Irish Oz (the indica I've been smoking which is very high-grade) any day.

I presume that indica would be best for people with pain, who are using marijuana for it's medicinal purposes. Your mind doesn't really get cloudy, and you don't forget things as much, you just feel numb, warm, relaxed, and very comfortable. If you want something that will be fun, get you baked and blazed, and feel good, I'd go for sativa, or some sort of hybrid.

I've only been smoking for around a month, so I'm still a beginner, but I hope I helped answer your questino.
Peace,
horror business