There are a few things you need to be aware of when it comes to water conditioners. First off, find out exactly what is in your tap water. Conditioners vary in what they may or may not do, but contrary to what the manufacturer will say, they may be detrimental, depending. The more "involved" a product is, the more it is going to impact the system and the fish.
I agree with essjay completely on the "extras" like slime coat production, aloe vera, etc. There is absolutely no evidence that aloe vera is beneficial in an aquarium, so that means it may do nothing or, more likely, it may be doing something negative. One conditioner contains valium...now why would we want to be drugging the fish? All of these additives should be avoided.
I was using Kordon's NovAqua for years, until I changed to API's Tap Water Conditioner earlier this year. I only have chlorine in my tap water, so the only thing API does that I don't need is heavy metals, but nearly every product detoxifies heavy metals so it is pretty much unavoidable. API does deal with chloramine by the way, they advise a larger dose than just for chlorine; most reliable conditioners will today treat chlorine and chloramine, and I am not aware of this being an issue. Prime was mentioned, and there are certain situations where this might be the best choice; ammonia, nitrite or nitrate in the source water, or during the initial cycling. But if you do not have especially nitrite and nitrate in the source water, there is really no point in using this product; the fact that it messes with the nitrifying process, and that Seachem cannot adequately explain how this occurs with respect to nitrite and nitrate, bothers me. I do not like dumping unnecessary chemicals into an aquarium. These do impact fish.
The other thing to be aware of is the concentration versus cost. Products that are highly concentrated, such as the API and Prime, use much less than most others. So while the initial cost may seem more for this or that bottle size, it works out much less expensive over time because you are using much less. I am not aware of any product as economical as the API Tap Water Conditioner, which treats 20 gallons with 1 ml. And if you only have chlorine or chlorine and chloramine, this is by far the best product to use.
Once you settle on the best conditioner, buying it in a larger size is also saving money, as these will be less per volume. Also, you can order many online. I try to patronize good local stores when I can, but I also have a very limited income and when I can save more than $200 over a year, I do it.
Byron.