White Widow is a classic - that's an excellent choice for a first grow.

Although you can find exceptions, Indicas are shorter, bushier & faster than Sativas.

You can find both varieties in the same potency range, but the difference is in the effect.

A pure Indica is more physical and can go all the way to couchlock.
Sativas are more mental - this can range from trippy to euphoric to energizing depending on what you're working with and how you react to it.

Many people who get anxious or nervous prefer Indicas - lots of other reasons to pick one over the other.

Of course, most varieties today are hybrids that offer a bit of both.

Before you make your next purchase, you should read up a little bit - lots of information on this site and the Internet in general is filled with good stuff.