Dean Grennell retired long ago, and am not sure if he's alive. He was good on reloading, and a nice guy in person.
My classic favorites are Jack O'Connor, whose droll humor and sophistication I admired, Skeeter Skelton, and Elmer Keith.
The best and most versatile of the current crop is probably Brian Pearce, at, "Rifle" and, "Handloader".
When he isn't doing a review because it was assigned as opposed to writing something he really enjoys, Jim Wilson is good. Bit too folksy at times...
Ayoob tells truths that some won't, lest they upset advertisers. His comments on how .38 lead SWC-HP bullets cleanly penetrate pig skulls and give clean kills, where .380's fail were significant.
Frank James sometimes posts on the S&W forum
www.smith-wessonforum.com He'd probably be able to write more, but his comments about shooting his neighbors' cats upset many readers when he was regularly at, "Guns". Most of those readers don't have his experience as a farmer trying to protect livestock and poultry, and many appear to have been raised on Disney and PBS wildlife films. I think that I'd call my neighbor if I recognized his cat on my land before I shot it...feral cats are another matter.
John Wootters was more a hunting writer than a gun writer, but his gun comments are excellent. I was sorry to see him retire. He's knowledgeable about many subjects, including WW II aircraft and snakes, as well as guns.
John Barsness is basically okay, and his bullet articles are sound. He's a little too "down" on German optics as opposed to Japanese optics, though. His current, "Rifle" column neglects to mention that German rubber armor compounds tend to feel more solid and enduring than most Jap ones, and that German controls are more refined and smooth in use. Moreover, the insides of the barrels on Zeiss, Leica, and Swarovski (Austrian) instruments tend to be cleaner than on even high priced Japanese binoculars. Barsness also seems a little smart-alecy at times. He seems to have a healthy ego, but most gun writers are peacocks, so it may not be fair to single him out.
Lone Star