Obviously, it depends on what you want to do. I've got a few of these laying around, and they're good enough for a cool little emulation cabinet. Joysticks Buttons You can find the same buttons for cheap elsewhere. There's some really nice stuff here, but there's a price difference. Of course, the IPAC2 is pretty awesome.
I just bought two Seimitsu LS-32-02 joysticks and they're pretty decent at an affordable price. The buttons were the cheapest I could find (I'm linking to a danish site) http://www.arcadeshoppen.dk/knapper/standard-arcade-knapper/arcade-knap-groen.htm but now I think they're a bit clunky. They look good, but are unnecessarily large (the depth)
I use Happ joysticks (bat-top style) and buttons, because they are the style that were traditionally used in real arcade machines in the west.
As mholgatem mentioned above, many people (especially those who are into fighting games) prefer Sanwa or other Japanese products.
I don't know much about the Japanese style controls, but I believe the differences are that the joysticks have ball tops instead of bat tops, and the buttons are concave instead of convex.
To muddy the waters further, many older games such as Pac Man used ball top joysticks. Not only that, but some of the joysticks for these games were four-way rather than eight-way. This means that the joystick is restricted to four way movement only, ie no diagonals. This makes playing Pac Man considerably easier, but playing fighting games impossible!