I use tape and dope alternately and together depending on the application. Either should be reliable by themselves or together when compatible.
The biggest factor in threaded fittings is the quality/condition of the threads -- it's not reliable anymore, either due to poor manufacturing or damage from packaging/handling/shipping. Before I started ordering from reliable online suppliers, fittings I used to buy in stores were beat from packaging/handling and the threads had deformations, dents, or chips in them. That's just asking for leaks. They need to be inspected very carefully.
After that, it's all about snugging them up properly and not overdoing it.
My advice: avoid threaded fittings when you can. I never used to pay attention to it, but since threaded fittings have become less reliable over the years, if you can plumb something another way, do it. Not always possible but anytime I can eliminate the need I am happy. Especially on a PEX system that tends to be reliable (I've never ever seen a PEX joint leak) it's always a shame to invite leak points with threaded fittings.