Actually, the choices are fairly simple.  Both the Propex and the Platinum
Cat are good heaters.  The propex has a clean, out-of-sight installation
for $600-700.  A vented Platinum Cat gives similar heating performance for
$330 or so, but lacks the clean installation.  You pays your money and
takes your choice.  I've had both and liked both.  The propex is probably
more desirable and is what I'm currently using, but also more money.  

An unvented heater would have to be considerably cheaper than the Platinum
Cat's $330 before I'd consider it.

Bill
www.geocities.com/yosemite/gorge/1706