There's a 10 psi difference between my Nashbar Earl Grey floor pump gauge and Nashbar standalone gauge with burp button (the latter reads 10 psi lower). The standalone gauge is easy to use without losing air. It seals well and holds air. The only trick with Presta valves is to crack the valve open just enough but not too much.
Which is accurate? I figure it's like camera light meters. Check the same scene with three different meters, get three different readings. Photos from each usually look fine.
I just split the difference. If the floor pump says 100 psi, I call it 95. Then I go by how the bike feels on our rough roads. I'll pssst out some air until the ride feels comfortable but not sluggish, well above the pressure needed to avoid pinch flats (I weigh 150 now, down from 160 last year, and have never pinch flatted even blasting across unexpected or unavoidable rough spots).