Customer service is a huge concept. It includes answering phones, replying to email promptly, updated web pages, dealer network, knowledgeable personnel, representatives that do what they say, having items in stock that are listed on your web site/in catalog, offering only functioning items, prompt warranty repair/return, and I'm sure I'm leaving things out.
The BEST?...So far I like Knight and T/C.
The WORST...for me, White Rifles.