PapaDough,
The "best" world is a matter of opinion. Each world has different things that make it stand out.
Kiber Blue. This is the Oldest World. The original world, where the game first began. As such it has some of the longest running empires, and most experienced players in Simcountry.
Fearless Blue. This is the War World. There are fewer restrictions on warfare between players on this world. Rewards are higher. Players are more aggressive. Overall the planet is the most militaristic and dangerous in Simcountry.
White Giant. This is the biggest World. With more countries than any other planet. Being so large, creates deep and liquid markets. Making the economy more stable, and harder to manipulate.
Little Upsilon. This is the Private Enterprise World. It contains more CEOs then any other planet. The beating heart of the Enterprise and economic side of the game. Many players build vast private business,
Dan of DanNation said it all. What he noted about each of the worlds is correct. But it is up to each player to choose which world they are on. I started on Kebir Blue (5 years ago) but have since expanded to all 5 worlds. Now there is a cost to playing on more than one world (as only one world whether it be a country, empire or enterprise can be your main). You have to pay per month for any others.
Though one thing on Fearless Blue -it is not as dangerous as you think as not many wars have (recently) taken place there. However if you want a more peaceful and economic game than go on one of the other worlds.
I like Kebir Blue as it is where I started and my oldest countries are located. I also know a few of the players there. Each world is unique. Just do your research and pick one.