Out of the three, it would be a hard choice between EVO and Galaxy.
Both run 1GHz processors. EVO uses Qualcomm's Snapdragon and Samsung makes its own chip. EVO 4G has a 4.3-inch disply while Galaxy has a 4.0. However, the Super-AMOLED screen is amazing. EVO has a 8.0 megapixel camera and Galaxy 5.0. EVO has HDMI-out, connects to 4G, acts as it's on WiFi Hotspot, allowing up to eight connections and records in 720P. Most people would die for these features, but without a keyboard, some will simply move away.
It comes down to preference. I believe EVO is A LOT more anticipated than the Galaxy. Nexus One is still a great phone, though. But let's be honest, it's left in the dust by both of these power-houses.
Note: They all run 2.1, so you get the current up-to-date Android OS.