asking "which sensor is best" ... but giving not a single specification...
With more than 450 posts you should be experienced enough to give technical data and additional information.
Distance range, medium, temperature range, humidity, cost, frequency, resolution, precision, color, size, availability, power consumption.....
Ultrasonic waves undergo an air attenuation of several db/m which makes it rather unlikely to achieve a 20 m range at 45 kHz.
Acoustic level measurement in this range (e.g. for silos) is usually implemented with low kHz audible frequencies. Another problem to consider is temperature dependency of sound speed, also the possibility that the tank/silo atmosphere is different from air. All in all, verify if acoustic level measurement is suitable for your application at all.
Here is a sensor which can measure upto 40 meters. It uses I2C or PWM as output but price is high. If you can afford then use this sensor. I am going to buy one.