I would say the differences are sufficiently small between treadclimbers, treadmills, ellipticals and steppers that purchase should be based on other factors, such as:
-Which is more appealing to use daily.
-Which is easier on the joints.
-Durability - treadclimbers have been around the shortest time and have lots of moving parts, therefore they're the most potentially problematic for now IMO. Higher quality treadmills and pro ellipticals and steppers have proven track records of performance.
-Factors like space requirements, ability to fold, price, etc. On price, don't cut corners if the idea's to have something that will last; buying used on craigslist.org, ebay.com, etc. will help.
-Treadmilldoctor.com and other sources are helpful in determining which brands/models are best at various prices.