Greetings,
A capacitor with a working voltage of at least 48 volts will work. A 50Volt capacitor will work but as with anything pushed to it's maximum limit, it's life will be limited. A manufacturer may use a 63 Volt capacitor to save their $0.02c worth.
I am with Mstechca, I like to double the rating, so 100 Volts it is!
Also if it will be mounted near anything warm like a heatsink, large resistor or such, use a high temperature capacitor (105 degrees celcius) for longer life. I guess you are rectifing 120 Hz and not high frequency so ESR is of no consideration?