I would have to go with glass, it's the cleanest taste I think. No metal aftertaste, no burning papers.. just pure ganja. Although I definitely enjoy rolling up a nice joint and smokin with my lady.

On an interesting side note, when my girl and I first started dating I didn't think she smoked because everytime I'd pass her the bowl (it's what i smoke alone) but she'd always pass it up. Found out 8 months into it, she only likes joints. I got mad and yelled "We could have been smoking!".. she just laughed and I rolled a joint. It's been happy toking ever since.