My favorite method of training the core is through anti-extension and anti-rotation exercises. Planks, pallof presses and roll-outs of all kinds of sorts. Basic planks mean you should be squeezing your glutes and your lats to me. I often have clients coming to me telling me they can hold a plank for over a minute, as have many others. Cue them to squeeze their glutes and lats, if they can hold it with good form over a minute after that OK they win.
I'm not really crazy enough to believe that those exercises are enough to not get bored or address all the issues that come up with your core, not to mention it can just be plain boring. I find dead bugs, bird dogs and reverse crunches along with all their variations to be safe and effective methods for training your core. The regular old crunch...that gets tossed in the pile of no return. My reasoning is brought to you by Dr. Stuart Mcgill. Dr. Mcgill and his fantastic mustache, are found at the University of Waterloo in Canada where he has become one of the foremost, if not THE, experts on the spine. I've heard him a few times now, say that your spine has only so many flexions in it's lifespan, why use 10 more a day when there are other days? Not a direct quote, but the same time if he says it's a bad idea, I'm not challenging him with all the time he's spent looking at this stuff.
Lastly, hopefully this isn't a shocker to most of you out there. Training your core may or may not get you a 6 pack. The one place that you can earn your abs, is the kitchen. I don't have such a heavy desire for a 6 pack....I mean let's be real everyone wants one. That's not my goals for my training though. I don't want to look like the Michelin man, but my focus is on getting my lifts up and making sure I don't fall over during my sessions from exhaustion.
That's all I got today everybody, keep yourself warm and safe, and go out there and get after it...if you're not snowed in.