Both are useful. If you're just starting out, I would concentrate on getting a solid flat bench form ingrained in you head, and making progress with that. Then you can start incorporating different angles on press. Most incline benches are set to 45 degrees, but I prefer 30-35 to reduce pressure on my shoulders. Too high an incline, and you wind using more delts than pecs.
Mt Snow, VT - May 5, 2012 - Completed!
...i remain, he who remains to be...