Text originally borrowed from the Beatmania/IIDX/III FAQ on Bemanistyle, originally written by Kimcicle and updated by rmz.

Which style should I buy?

Every person has their own opinions about which style is the "best". Rather than point out a definitive list, I'll list the pros and cons of each style, and let you decide. It is easier, however, to get the newer styles.

beatmaniaIIDX 3rd Style

Total Songs: 81
Unique Songs: 50

Pros

  • Huge songlist
  • Beginner friendly songs
  • Can be found cheap used
  • Actual music videos

Cons

  • Timing is bad on certain songs (gambol, overdoser).
  • No beginner's mode (but there are enough easy Light 7 songs that you can get away with it).
  • Interface is widely considered to be poor compared to later titles

beatmaniaIIDX 4th Style

Total Songs: 53
Unique Songs: 28

Pros

  • Good song selection, with few songs repeated on other styles.

Cons

  • Expensive to purchase.
  • Light 7 songlist is significantly harder than other styles.
  • No beginner mode.

beatmaniaIIDX 5th Style

Total Songs: 64
Unique Songs: 18

Pros

  • Has a beginner mode.

Cons

  • Slower hispeeds than found on other games.
  • Many complain about timing issues.
  • Lots of songs are repeated on later styles.

beatmaniaIIDX 6th Style

Total Songs: 69
Unique Songs: 25

Pros

  • Also has a beginner mode (covers all the songs in the game).
  • Lots of extras in the game. Tatsujin videos. Movie clip mode.
  • Added hispeed 4.
  • Decent balance between hard and easy songs.

Cons

  • Songlist is hit or miss for people.
  • Notecharts by this time were getting harder, and this style reflects it.

beatmaniaIIDX 7th Style

Total Songs: 90
Unique Songs: 27

Pros

  • Good beginner mode.
  • Decent balance between hard and easy songs.
  • Fairly easy to get now.

Cons

  • Only 2 unlockable songs (Murmur Twins and Abyss The Heaven's Remix) and the 2nd one is hard to unlock.
  • Some complain about the sound quality, and say the style has an "incomplete" or "rushed" feel to it.

beatmaniaIIDX 8th Style

Total Songs: 90
Unique Songs: 49

Pros

  • Easy to get.
  • New sort methods. Other info can be displayed while selecting the song.
  • Balance leans a little towards the harder side, but beginner's mode can cover for it.
  • Random+ is entertaining.

Cons

  • Beginner mode restricts you to a shorter playlist than all of the songs in the game.
  • Lack of regular record screen as from previous styles.
  • Scores achieved in Expert Mode do not get saved.

beatmaniaIIDX 9th Style

Total Songs: 87
Unique Songs: 62

Pros

  • New high-res graphics make the game extremely pretty.
  • Quite a few first-time repeats (songs that have not been repeated before, including a lot from 3rd and 4th Styles).
  • Lots of remixes of songs from previous styles.

Cons

  • Not many revival songs, only 19 total.
  • Lack of regular record screen as from previous styles.
  • Only one preview song (No.13 from 10th Style).

beatmaniaIIDX 10th Style

Total Songs: 88
Unique Songs: 62

Pros

  • Newest IIDX title.
  • Happy Sky-style Hi-Speed modifier allows for fine-grained mod control.
  • S-Random is more entertaining than Random+ - luckily, both are included.

Cons

  • Difficulty skews very high on 7-Key.
  • Lack of regular record screen as from previous styles.

beatmania (American release)

Total Songs: 58
Unique Songs: 24

Pros

  • Easy to find
  • Comes with controller
  • Beginner friendly
  • Contains many 5Key songs, which have yet to appear in any of the IIDX CS releases
  • Ability to save replays of your performance

Cons

  • Grades are artificially inflated from Japanese and arcade releases
  • Some songs have changed notecharts
  • Total amount of songs is low compared to recent releases
  • Only 40 of the songs are actual IIDX 7Key songs
  • 5Key songs only have one difficulty

Which controller should I buy? I can't afford a controller right now, should I just play on a Dualshock?

Personally, I would wait to have the cash to buy one game and the controller at the same time. However, if you are -that- pressed for cash, I'm not stopping you from playing on a Dualshock. You won't get the same experience, however, and playing on a Dualshock is confusing as hell.

As far as buying controllers, there are a few options:

Konami Controller - An official controller by Konami, runs for about $90 from most online retailers. The keys are spaced correctly, but the turntable is smaller and closer to the keys. The keys are switchable so that you can emulate both the first and second player sides. People have problems with sticky keys, but you can mod your controller to get around these problems.

American Controller - Also made by Konami, this controller comes bundled with the American beatmania, which usually costs $60 or so for the game and controller. It has some slight differences from the Japanese controller mentioned above; most are cosmetic, but it is worth noting that the buttons are curved outwards, and are therefore much less prone to sticking. Though it comes bundled with the American beatmania, this controller is fully compatible with the Japanese versions of IIDX.

Rave Discman - Don't buy one. The price is attractive, but frankly, it's not all that great. For one, the keys are the wrong shape and are not spaced correctly. It's better to hold out for a Konami controller. It's possible to use a Rave Discman as a base for your own ASC, which some people on the forums have done. Take note this controller also has some voltage issues which could fry PS2->USB convertors that you might use.

Konami ASC - The official arcade-style controller by Konami. It's huge, it's pricey, and for some, it's worth it. The price tag is quite hefty, but with arcade perfect dimensions, clicking keys, and switchable from first player to 2nd player, lots of people have purchased them. Expect to pay around $450 when all is said and done.

Third-Party ASC - two controller makers well-known in the Pop'n Music community have both started producing ASC-like controllers for IIDX.

There's a port on the side of my beatmania IIDX controller and I can't fit my finger in there? What is it for?

The port is meant for a foot pedal for beatmania III, but no home versions of beatmania III have been made. You can plug in a pedal from the drummania home controller into it, and triggering the pedal acts as a scratch. Cool, but mostly pointless.