Hi calzone,
It's totally appropriate to discuss competitors! I'm always keen to hear what my customers' choices are, and how I can (<ahem>) influence them
First of all, I want to state up front there is no "correct" solution overall. If someone thinks that everyone should ____ ("be on PC" / "use XYZ app" / etc), then they haven't understood that everyone has different needs. There's a correct solution for *you*, and only you can find out what's best for you.
Regarding what printers Wifibooth support: Wifibooth supports any AirPrint-compatible printer (that means, a printer that you can print to from your iPad from the native Apple Photos app, ie. doesn't need the printer's own app), DNP printers via a DNP WPS product, and printing via FTP (many print servers support this). Your "guys at the store" should have heard of DNP, as they're one of the most popular & best-selling photobooth printers in existence. DNP printer + DNP WPS unit is a powerful combo.
It is great to hear that Snappic will finally be getting DSLR integration! I welcome the competition. Can't wait to see what they license it for

-- Wifibooth already has this functionality and fits in-between their top two tiers in their current pricing model, which currently appear to top out at $1600USD/year (source: getsnappic.com). Wifibooth by comparison is
over 10x cheaper per year. Of course that's not apples-to-apples: Wifibooth is very different than Snappic; different features, different design, and different philosophy too. That's ok: more choice for you!
One of the things that's very important to me, and therefore a major point in the design of Wifibooth, is simplicity. Not just the app: the simplicity of going from an empty room ("where are the electric sockets?") to a fully setup photobooth. This is why iOS/iPad is a far superior platform to Surface: when was the last time an iPad told you "Sorry, you can't do what you want to now, I need to reboot to install updates now!" --- never. That's a Microsoft problem. It's also important in the ease of connecting the app to the camera: many competitors have an iOS app, but they ALSO require a computer that handles the connection to the camera. That's one more point of failure, more equipment to lug around, etc. Wifibooth is simpler than that. The app echoes that: how many touches in Wifibooth to start a new event? To connect the camera? To change settings? Very few
Finally there's the issue of internet access while being connected to a camera, ie. for dropbox uploads, email, and the like. I'm not sure how Snappic will solve this, but it isn't easy unless you force people to have complicated portable networking solutions on-site. This is because the majority of cameras (all except Canons) will only support a single incoming connection to the camera, which means it's not possible for the tablet to be on the internet at the same time (well, Surface may have better support here than iOS, not sure). Wifibooth has 2 unique ways of solving this problem, both of which took a lot of time for me to develop:
BluePrint, which allows you to have your iPhone run the printer on the wifi network, and communicates over a custom Bluetooth protocol I designed to Wifibooth to make it simple & efficient to print while your iPad's wifi is connected to the camera; and, true offline support for lots of functionality, including Dropbox and Email. This means that if you're unable to have your iPad connected to the internet and the camera at the same time, then you don't have to forego Dropbox/Email functionality: these are stored in the app, and automatically uploaded as soon as internet access is available. This is complex, difficult, and time-consuming to develop -- I know of no other photobooth apps that support this.
In short: the app is really just a small part of the overall photobooth picture. Which cameras will Snappic support? How will you have internet + camera connectivity at the same time, and what extra hardware / connections will you need to support this? Wifibooth's story is clear already, and focused on simplicity.
(Re PBX: this year i'm so focussed & busy developing new features for Wifibooth, I don't have time for PBX -- will think about it for next year! If you go, let me know how you felt about it..)