You'll have to decide on what combination of distance sensor + microcontroller you want to use. I've tried them all, and found the following configurations to work well.
- Trinket + Parallax Ping)))
- Trinket + Maxbotix Proximity Sensor
- Trinket Pro + HC-SR04
- Trinket Pro + Seeed Studio Ultrasonic Ranger
Of all the sensors that I tried, the Parallax Ping))) was the easiest to use with Trinket. All you need is GND, VCC, and 1-pin for measurement.