I've tried many indie RPGs. They are very nice games, but I'm looking for something to develop a long-term campaign.
Is Apocalypse World suitable for it? Or is it good just for an adventure?
Absolutely. Apocalypse World (AW) is tonnes of fun to play for a single session, but it was actually designed for long-term play. The full possibilities of the character-development mechanics require several sessions to unfold.
There are three common lengths of Apocalypse World games.
Single session. These are fun, as already mentioned. This is a good way to introduce the game. You get to experience the innovative resolution paradigm and mechanics, and you do get to explore the character and world to an unusual degree for a single-session game, but you don't really get to see the characters grow.
A single story arc. This is the typical "long-term" game of AW, and the longest I've personally played. We had two (sometimes three) characters, and we went from just trying to survive, to dealing with rebellions (one of us was a Hardholder, the other a Hocus), to going on a quest and uncovering the nature of the Psychic Maelstrom — and then we killed it. It was epic. That game lasted a dozen or so game sessions over a few months of play.
A single story arc is enough to really get your teeth into the characters and world. You get to see hard choices made, maybe changes of PC philosophy, and you have the chance to significantly affect the world. It's long enough that the PCs can get enough advances to start taking moves from other playbooks, and maybe even pick up a new playbook entirely.
How long is a single story arc? It ends when the Big Stuff That Is Happening wraps up in a satisfactory way. AW just generates Big Stuff (at least, big to the characters), and when you're in the middle-game of a campaign of AW you'll start to see the interesting events start to agglomerate around a particular set of larger-scale conflicts. It's just how the game tends to play. When that larger set of conflicts resolves, you'll find there's a pause – a breathing space for the characters – where it feels natural to just end the game.
An ongoing campaign. This is what happens when you don't end the game during that breathing space. You keep going. You maybe skip a year of in-game time and Ask Questions* of your players about the intervening time. This is just like starting a new campaign, except you have existing characters and you already know a lot about the setting. (This is a good time for people to have characters retire to safety† too. You don't have to have all the same characters.)
This is how the designer, Vince Baker, runs Apocalypse World, and it fully supports this kind of ongoing play.
The wonderful thing about AW is that you don't have to plan an ongoing campaign. There's no difference between a one-shot session and a campaign's first session, so you just play one sit-down game of AW. If the players want to keep going, you play an arc. If they want to keep going, you have an ongoing campaign.
You don't have to do anything different as the MC, either.** So since you don't plan the campaign ahead of time, the prep for the first session or a one-off session of AW is the same. Prep before the first session is actually non-existent, beyond reading the book and printing out the play materials. (Make sure you have a copy of your Agenda, Always Say, and Principles. Read and re-read them!) Prep for the second session is more involved, but it gives you the seeds of an entire story arc.
So run a first game, and see if the players take to the game. Use and fill out the First Session sheet while you play (p. 122 for details on the First Session). If they do like it, do the After The 1st Session prep (p. 132) and run a second session. If they like it, you've got a campaign.
* This is referring to one of the MC's Principles: "Ask provocative questions and build on the answers."
† One of the possible advancements for a character.
** The most important thing about AW is that you do not plan a campaign. Do not. The rules actually forbid the MC from doing that, and your players are completely in the right to call out an MC for cheating if they pre-plan the campaign. (If this is confusing, it'll make more sense after reading the game book. A core principle, and an assumption that all the game mechanics are built around, is that the MC is not pulling strings to make the game follow any particular plot. The game simply doesn't work if you pre-plan plots.)