There are an awful lot of opinions on this matter. By providing a little more information, you will be able to help narrow down the breadth of the selection process. First and foremost, you were told correctly. The Knight's and B&T cans are the only ones that are not warranty voiding. That doesn't seem to bother many folks.
You will want to choose between a light weight can and a can with a booster (LID device). On the light weight side, you're going to want one below the 7 ounce barrier. I've found that to be the point at which boosterless designs give me trouble.
What application are you contemplating? Is this just plinking at the range or at tin cans... or do you have a hunting application in mind. Weight and type of bullet make a big difference. Are you intending on shooting the can dry, wet, combination... First shot pop a big deal or not, etc. There are a LOT of really good suppressors available. Not every one is going to perform to expectations in every situation.