I use a Plantronics M25. Got it at walmart for $28.
Its the first bluetooth I have used so I don't have anything to compare it to but I am happy with it. I primarily use it to listen to music and podcasts while driving my truck and Siri works well about 90% of the time.
I drive semi trucks so its very loud in the cab. People I am talking to can hear a lot of engine noise but can still hear me well. And the volume level is good enough to hear with the engine revving and jake brake rattling away...
I also love the features of Bluetooth V3 and A2DP that lets me listen to podcasts and music through the earpiece.
The battery life is pretty good. I can listen to podcasts for a whole 10 hour shift and take a few calls and the battery has about 10% left. BTW, with BT v3 the iphone 5 shows the battery level on the iphones screen.