Who would you assume to be more possible to father a child? A man with a vasectomy for 10+ years or a man with no vasectomy that used the withdrawal method?

Unusual question. Vasectomy, if successful (((% are) means that no sperm escape with ejaculate. Sperm aspiration by needle or vasectomy reversal would be required for insemination. Withdrawal method is totally unreliable as sperm can enter vagina in pre-cum which occurs before ejaculation (climax) ; without sensation. Thus withdrawal method frequently results in pregnancy. Post vasectomy pregnancy occurs rarely.
Withdrawal. Even teens know that the withdrawal method of birth control is not effective. 30% of couple who try the withdrawal method become pregnant. I am surprised by your question. Pre-cum is semen and semen has sperm.
Withdrawal Man. Pre-jaculate is know to carry sperm. Betting on pre-climax withdrawal to guard against pregnancy is not a good bet. It is a better bet that the person with a vasectomy isn't the father.