Top 20 coins is always a good place to start.
Before you start investing i'd recommend you to read alot! Articles, charts etc. (Remember bitcointalk is the best place to start

)
Here is what i did when i start:
I found a top 20 coin, found a coin with reasonable price(From my pow), and started reading about it.
Read read read - read some more - think about investing then read some more

The top coins are fine and should make up the bulk of your portfolio but the real insane gains are found on the low marketcap coins. These are the ones that have a real chance of going 100x or higher but its a very risky thing to do.