As others have said, rather than there being a best, there are many very good programmes with different qualities to suit different people. Last year I downloaded a trial of
Genbox. After playing about with it for a month or so, I decided I very much liked it but not at the price it then was. However, a few months later, the price has dropped and the other week I bought a copy from
TWR computing. It comes as a single disc in a plastic sleeve, no fancy extras, but suits me fine because of how flexible the programme is and how well it deals with a variety of situations within a family (eg 2nd marriages/families, siblings from family A marrying siblings from B, adoptions, etc).
Shirleymarye, you might find this is just the job for your cousins marrying cousins. It seems to cope well with the less than straighforward situations thrown at it .