I use nothing but the Osram +30 bulbs from www.powerbulbs.com. Never have had a fialure with them or the Phillips equivalent for that matter. The most important thing to remember is NEVER-NEVER-touch the bulb glass. Also make absolutely certain to reinstall the rubber boot correctly.
Six months is much too short a time frame for most any bulb. You also want only 55 watt lamps. The Osram I use are rated 55watt=100 watt equivalent because of their design.