Depends whether you want a desktop or an industrial-strength solution. Interbase is fine if all you want is a small discreet desktop datbase solution similar to MSACCESS.

If on the other hand you want the speed, power, scalability and robustness offered by a mainstream RDBMS then choose SQL Server over Interbase everyday.

Don't get me wrong Interbase is a good robust product, but in my opinion, it's a question of size (isn't it always?) Interbase is a good 'Home' solution, SQLServer (and for that matter ORACLE) are profesional enterprise solutions.

I have found it is possible to please all of the people all of the time if you do exactly what they want. Harold Macmillan 1961