I don't think guys were given the choice about recruitment into the Forces or being a Bevan Boy. But, the Bevan Boys did a valuable but dangerous job during the War and have been recognised over the years and are invited to march on Remembrance Day at the London Cenotaph.
I knew a guy from Sunderland, now deceased, who was a Bevan Boy. He joined the RAF after the war and admitted that he would have preferred to have been in the RAF during the War than having to go down the mines.