Permission to compare products of different companies on my website

I would advise you not to say anything which demeans the product or the company or then they may slap you with a legal notice which would be a pain to defend. The maximum you can do is give a comparison of the rates offered by each company without saying anything derogatory about the company as such. Such websites are already there like comparehatke.com etc. So instead of saying that so and so company uses unfair means you can just give the price charged by that company so that the consumers can make an informed choice.

You can advise the people by using the name of the company, its only ur view in regards to the services of that company. But make sure that you opinion must be based upon on true facts and u must have a proof to that effect. You are also required to make disclamer with your every post.