I developed a point of sale program for a shop with Delphi and at first used BDE as the database system but it didn't seem very reliable and I changed to Absolute Database which seem to work a lot better but is still not 100% reliable as it seems that when they get really busy (they have 2 PC's with scanners), it drops a sale occasionally.

It might be the PC's or my own not perfect program which causes the problem I supposed. But I would like to know which database system would be the most reliable to use for this program of mine? Any advise?

Any of the tried and true database servers would work. MSSQL Server or MySQL, for instance.