I'm no expert, but I'd say the following gauges, in order of importance:
1. Wideband A/F
2. Fuel pressure
3. boost/vacuum
The 3rd gauge would read vacuum and boost, so it would go from around -25 inches of vacuum up to around 20 psi of boost.
My new Stang doesn't have a supercharger, but I ordered a Stewart Warner boost/vacuum gauge from SummitRacing.com. I got the SWW-114545, because I wanted a 2 5/8" gauge: