#1 DO NOT buy an Ab if there is not testing data associate with it, if you are not desperate for it. Plus, if you want to detect an endogenous protein, be cautious with an Ab tested only with recombinant protein.
#2 If you have several options, go with the one that can be diluted more.
#3 If several companies carries the same Ab, you can get it from a smaller company that usually offers a very better price.
#4, Use searching engine to shop around before you buy an Ab you are not farmilar with. Here are two good Engines I like to use.
Be advised the information search engines sometimes is not very very updated. If you can not find an Ab from Any ENGINE, DO NOT give up. Check the websites of some big Antibody carrier manually to see if is already in their line of new products.