This is most of a post I wrote in another thread:
IMO, Calypso is the best planet for new players. It has a long starting mission chain designed to feed you enough ammo and loot (if you pay attention) to keep you going without having to deposit until you finish the Camp Phoenix missions and you're about level 10ish in some combat skill, probably laser rifle. It introduces new players to things like instances, beacons, iron missions, wave events, and EU's own particular take on PvP. Caly is the largest planet, with the most people and the largest economy. That makes it easier to buy and sell things. Not easy, just easier.
Ark is the second most populated planet, and I think the second largest. It has the second largest economy, which means it isn't impossible for a newbie to sell things there. Ark has a very dedicated player-base, and newb-friendly mobs. For a new player, the one thing that really characterizes Ark is a very linear mission experience. EU is basically a sandbox game with missions...it is pretty open as far as goals. Players tend to make their own. But if a player is someone who always likes knowing what to do next, Ark missions funnel you from new player, to beginner player, to experienced player, to fairly advanced player in their main mission chain. That isn't to say that you have to stay on that path all the time. There is plenty to do on Ark. But if you enjoy achieving goals that are set by the game, maybe Ark is the best planet for you. Note, that main mission chain is gated. You need an Ark passport to do it. Players born on Ark get the passport free. Players born elsewhere have to pay 10K sweat to get it.
Rocktropia is the second planet started. It stumbled pretty badly out of the gate, but has retrenched and come back strong in the last couple of years. The RT starter missions are pretty pedestrian, and for a long time they were broken. But that didn't matter, because the real starter mission chain was Hunt the Thing, widely held to be one of the best and funnest mission chains in the game...possibly the best and funnest. Rock doesn't have that many people, so it can be hard to sell loot there. Having said that, there is a lot there for the new player...haters to sweat, vixens to grind, and zombies to kill. You can also hunt papoo on Secret Island, just make sure you have a banana to get back. The main thing to note about starting on RT, is that you don't. Neverdie made a deal that players that start on RT go to Thule, and then to Caly, which I think was pretty damned decent of him. So starting on Rocktropia is exactly the same as starting on Calypso, with two exceptions. One, your avatar gets a cool looking tee-shirt, which looks better than the OJs. And two, you get a one-time, one-way teleport to Rock from Caly. Do NOT talk to the npc unless you are ready to go right then.
Cyrene is struggling with development. Technically, it is still in open beta. Kris works hard, but it is still pretty buggy in places. But there are players that love it, and some great people who hang out there. There is quite a lot on Cyrene for new players, but it is all very poorly documented. You can find it if you look, and ask around in chat, and the planet is certainly worth a new player (or any player) spending some time on, but it is probably best to actually start somewhere else, where it is easier to learn the game.
Toulan is also new, still in beta. I don't know if you can start there. I know some people have, but that might be closed now, or only open to certain regions. Regardless, there are fewer bugs than Cyrene, but also even less people. It has a really good and fun starter mission chain, and good mission mobs for beginners, but the economy is just too small right now for starting players to do well on Toulan, even if they can start there.
Next Island...is peaceful. Again, I don't know if you actually can start there now. I don't think so. If you can, don't. It's a nice place to visit, but not to start.
Monria, starting on Monria was disabled while things were in flux with the sale. When you could start on Monria, I believe that you began at the Calypso tutorial, but instead of going to Thule to start the Caly mission chains, you went to Monria and did their starter missions. The starter missions on Monria are okay, but other places offer more.
IMO, start on Rock. Do the Caly missions, learn the game, and when you want to go to Rock, talk to the guy in the Sky Lounge in Port Atlantis.
If it's Caly, start with the missions at Camp Icarus (but go to Thule and at least get the Valk). If it's Ark, start at the new arrivals TP if you have 10k of sweat (you can sweat it yourself or buy it). If it's Rock, start at the Hyperplex and Newbs Newbs Newbs (and Hunt the Thing). If it's Cyrene, start at the rookie training area. If it's Toulan, you'll know where to start. If it's Monria, start at the Hub. Don't start on Next Island.
