I've choosed Firebird - Windows server, because is very easy to download/install (3M download). It has the same feature list as Interbase because is based on Interbase 6 code, ported to C++, with many improvements and bugfixes . Has precompiled binaries for Linux, Windows and other OS-es. And it is 100% free, even for commercial distribution. The only thing I don't like about it is the lack of Logical datatype, must be converted .
Didn't tried PostgreSQL (hard to find precompiled binaries), but I heard that is an excellent RDBMS.
MySQL is very fast, but it has has no subqueries,stored procedures,triggers or foreign key constraints and only has table-level locking for (native) MyISAM tables (writes block reads and reads block writes). Also, doesn't support transactions on native tables. You can achieve transaction, row level locking and foreign key constraints support only using BD or INNODB tables.
Good luck!


>Hi,
>
>Thank a lot for the additional information.
>I am comparing the feature and going to evaluate them.
>
>However, which one do you like best, why ?
>And which one you don't like, why ?
>
>>Go to www.ibphoenix.com , you will find a lot of useful informations about Interbase and Firebird databases (Downloads, KnowledgeBase, Examples, Articles, etc.
>>Maintenance for Interbase / Firebird databases is easy because it is one file database (if database is very large, it can be splited in multiple files on different volumes). You can do online backups, rebuild index, etc, with users connected to database.