I use PL/SQL Developer for running multiple queries and stored procedure development, as it's rock solid, and you can kill the process via Task Manager, and get back all your windows upon starting up again.
I use TOAD for browsing, as that functionality can't be beat. But it's flaky on me, hanging, etc, although that is probably my computer..
I would buy both. I have both open now.
For accessing odd sources (OSISoft PI, JDE on AS400, 4D, Access, Excel), I use Advanced Query Tool. It's great to be able to use SQL against an Excel sheet of a proposed table, to create your DDL.
