I would go for glass. Because the hits are alot clearer and there much easier to clean then a metal pipe. I got mine on eBay....It went fine, was shipped to me house and all so if anything go for a nice lil glass pipe. Should be around $20 in all.
http://shop.grasscity.com/shop/grasscity/set1.html i loved this little set so much i bought 2 of em. the pipe hits so nice and you get all the other stuff and its only 15 bucks. great buy!
definately glass, glass is pretty damn durable for the most part as long as you dont purposely drop it or throw it around(not like you'd do that anyways) If anything, go with a nice thick glass spoon or chilum, they're really durable, i use to have a thick inside-out glass chilum and i dropped it all the time, it would get tiny pebble chips and dents in it, but never broke.
If you get glass, be sure to get one that is hand-blown and not machine blown. Machine blown glass pipes are alot cheaper, but they break if you drop them 1 foot off the ground. The sound that makes is sickening, its like this weird horrible crunch, like dropping a baby on its head... but i digress. If you want concealable, a bat is a good way to go, it's a metal pipe that holds like 1 gram of weed, you are supposed to take 3-4 hits at a time over a long period of time, it gets you fucked up. But of course there is the classic metal bowl, you can get a midget one for cheap, it doesn't break, it's small and easy to clean. The bitch part is that the weed taste off more than it would with a metal bowl. If you want fucked-up get a steam roller, those things will kick your ass.