Luckily, conditioner, being one of the few LFS items with a true and usual need (assuming you want to lower risk) also happens to be a product bottled by many manufacturers but where beginners will generally be ok with whatever bottle they first bring home. It may not be the best choice in the long run but its usually ok that first time.
The discussions on TFF generally center around two topics:
1) the concentration
2) the extra features
The vast majority of suppliers use sodium thiosulfate as the chemical to take care of chlorine and chloramines (and more or less all of them take care of either these days) so the behavior is pretty similar for all of them I believe. This chemical does its neutralizing job pretty much as fast as it can spread in the container its been added to. Since neutralizing chlorine or chloramine (whichever your water authority has) is by far the main job of a conditioner, you might as well use up whatever you bought because it was first recommended.
Hobbyists who keep tanks for years and those who have lots of tanks begin to pay attention to the cost-per-gallon because of the expense of the product. To really compare costs, you need to know how much of the product is needed for each gallon or liter of water treated.
By "extra features" I mean the temporary neutralizing of ammonia and nitrite and the binding of heavy metals, although there can be other things like slime-coat maintenance. My reading over the years leads me to believe there can be quality difference among products with respect to the more important features of temporary ammonia and nitrite neutralizing and the binding of heavy metals, but I do not have references to back this up.
The most common advice you'll see here in the beginner section is to us Seachem Prime, due to its high concentration with resulting low cost per water unit. My one bottom line recommendation is to definately use Seachem Prime for the first two years as a beginner, both for its savings due to concentration and also because I believe the extra features to be of very high quality. After that, if one is still thinking about the concentration question, the various pond dechlor products should also be compared as some of these have high concentrations. After two years the typical biofilter is much more robust and probably there will be less need for the extra mini-cycling help the extra features provide. Recommended dosing for beginners is 1.5x to 2x whatever the instructions say but not more than 2x (the main function of dealing with the chlorine compounds is all about lowering risk, and the risk can vary depending on what local water sources do. Sometimes local tap water is "shocked" with large extra doses of chlorine/chloramine.)
There are a few aquarium web sites out there that have kept written reviews of various conditioners over the years.
~~waterdrop~~
