Hello,
My favourite is ADOdb, mainly as it seems to be the fastest of the DB
classes, has solid transaction support, a convenient quoting/escaping
method, and a whole host of other handy features (like generating a
form dropdown with the results of a query for you). Caching queries
on the webserver is also nice, as you don't have to make the
round-trip to the database (like you would with MySQL's caching).
Most importantly is the XML goodies that are with the most current
releases of ADOdb, which allow you to reverse-engineer a schema
dynamically and then make alterations to that schema, and then apply
them to your database again.
Quite impressive.
If you do not like the syntax of ADOdb, then PEAR's DB is my second
recommendation, as it has just about everything you would need out of
a DB class.
-- Mitch