Depends on how much you want to spend. If you have lots of money and want shiny bling, get a titanium one. The Moots is a very nice post...I already got one and et iz vaery neice If you have lots of money and don't mind putting up with the care and feeding of a carbon post, get one of those.

If you don't have a lot of money but still want to save a little weight, go with aluminum. Aluminum is actually lighter than titanium, although most titanium parts are thinner than aluminum so they end up being about the same.

If you only have 2 nickels to rub together and you just dropped one, go with steel.

But from a comfort perspective, it really makes no difference...unless you go with a suspension post