What is the best medication for hbp and ED for a 73 year old with slightly enlarged ptostate? I am corrently on aldomet (methyldopate) 250gm twice daily

Many options. Other option is to use doxazosin (Cardura) or Hytrin (terazosin) that are good for both HTN and enlarged prostate. Remember that hypertension requires three, four or more different medicines (once, twice, three or four times a day) to achieve good control over several months. So it is very likely to add others like acei, arbs. , betas or ca blockers.Aldomet (methyldopate) is currently not commonly used in the US.
An ACE or ARB class. Aldomet (methyldopate) would be likely to cause ed. Methyldopa was a good drug 30 years ago but is seldom used today because of side effects. I would consider using Lisinopril + hctz or losartan + hctz and add tamsulosin for the bph.