I am a fan of Virtual Pinball (and continue to use it), but I still find "The Pinball Arcade" essential.
1) The Pinball Arcade gives me a legitimate way to license the tables. Free demo versions that allow one to play up to the first high score are also available for each table.
2) Like Virtual Pinball, The Pinball Arcade's tables are recreations from real tables that I grew up with. They are not impossible virtual creations that are made much easier in order to expand pinball appeal to a larger audience. If that is 'your bag', check out Pinball FX2.
3) Although much of this subjective, The Pinball Arcade's implementation feels more polished than Virtual Pinball. One example is how the lighting on the board is 3D rendered. The Virtual Pinball table’s lighting effects are statically added using an image tool. Although the ball physics could probably be proved to be superior (one way or the other) mathematically, I can only say that I find the ball behavior of The Pinball Arcade to feel more realistic. That is not a slam. I would expect that a product that had developers paid to work on it all day every day would have more polish than a product whose developers are contributing “as they have time”.
4) Plug and Play. Download and launch. It’s that simple. On the other hand, Virtual Pinball takes quite a bit of R&D to get going (even with an abundance of available documentation). That said, VP is worth every bit of blood, sweat, and tears that are required to it going.
5) Supporting TPA (The Pinball Arcade) is really good for the game. The fact that is available on just about every mobile platform has really rekindled pinball interest with the masses.
1) The tables are pretty expensive unless you buy a season at a time.
2) The tables are not stored with a "Pinball Arcade account"; but rather, the store for which you purchased the engine that plays the tables. On one hand, I would expect to be able to buy the content in the cloud (like an Amazon kindle book) and then play it on any device that had the kindle app (buying the version of the app native to that platform if necessary). On the other hand, extra maps for Call of Duty on PC, Xbox, and Playstation do not transfer between each other. At $30 a season, you really have to pick just one. I am probably choosing Steam as my store since I can at least go from PC/Mac (with XArcade Tankstick) and use a Netbook on the go. On the other hand, I'd much rather use a tablet for mobile. So, I may go with TPA on iOS for mobile and stick with VP on the desktop.