I've found hybrids like Blue Dream are useful. Not too sedating but a very relaxed sort of focus.
Tons - there are over 70 cannabinoids last I checked (which was several years ago, and we've discovered more since). They all have different effects. Some aren't even psychoactive at all.
The indica vs. sativa is a rough way of describing the relative ratios of the various cannabinoids. Not all indicas and sativas are the same, and some sativas might be more sleep-inducing than some indicas, but it's easier than enumerating chemical compounds which have rather unfriendly and unmarketable names.
> How do you know which is which?
Ask the person growing or selling it to you. If you live in a medical or recreational state (Colorado, California, etc.), they will be labeled as pure indica/sativa, or a hybrid (and if a hybrid, which one is dominant).
Recent studies have shown that reported genetics aren't very reliable (ie. what is claimed to be a pure indica or indica dominate hybrid have actually tested as ~75% sativas).
The combination of compounds is probably the biggest driver in a person's experience and the percentage of indica vs. sativa only has some influence over that combination.
Mood and delivery method can alter the effects, too. If you're taking massive bong hits after a long day at work it'll be a lot easier to fall asleep than if you're hitting a vaporizer early in the day.
We got some pure sativa here : White Widow : lifts you up, very energetic. No couchlock at all.
If you smoke pure Indica, or Indica dominant strains then yes, you are likely going to be knocked on your ass and get absolutely nothing done.
But if you smoke a Sativa, or Sativa dominate strain, then you'll find that your focus goes way way up, your ability to dig into problems and solve them goes way way up, and generally you get a ton more done.
Reading this article and then the comments on that site it's pretty amazing how poorly people understand pot still.