Toilets come in many styles, shapes, sizes - and prices. Most options are more decorative than functional, but some choices are significant. A higher bowl height can be easier for people with back or leg problems. And, for existing bathrooms, you'll need to match the "rough-in" measurement (the distance between the center of the flange around the drain opening and the wall behind it). You can add blocking between the tank and the wall to accommodate a shorter rough-in measurement, but you can't install a toilet designed for a longer rough-in measurement without complicated alterations to the drain line.
Tanks with a gravity flush system (with the common fill valve, flapper, and overflow assembly) are usually less expensive than pressure-assist units (with a one-piece plastic chamber inside the porcelain tank). Pressure-assist units can flush more efficiently, because compressed air pushes out the solid waste. However, while parts for a gravity unit can be replaced easily and inexpensively, when a pressure-assist unit fails, the flush unit inside the tank - and sometimes the entire tank - must be replaced.
Especially with water-saving toilets (current federal standards mandate no more than 1.6-gallons per flush), it's important to look for a better-quality model with a larger-diameter trap. Make sure the toilet is glazed throughout, including all surfaces of the trap. A siphon jet (included on nearly all current models) will eliminate solid waste more efficiently.
In addition to the toilet, it's worth purchasing 5/16" bolts (instead of the 1/4" bolts generally provided) to attach the stool to the flange. Both these bolts and the tank bolts (used to mount the tank to the stool on a two-piece model) should be solid brass - not brass-plated steel, where the heads can rust away.
source: http://www.cleveland.com/cleveland-heights/index.ssf/2015/03/check_out_options_when_buying.html
by Becky Stager, Home Repair Resource Center
http://www.thisoldtoilet.com
