From my experience in military modelling, most people there would not touch the gundam markers.
For panel lining, I have several ways, which one to be used depends on my mood I guess:
+ Oil/Enamel paint wash: this one is mostly for serious modellers since they're quite problematic
+ Acrylic wash: less problematic since there is almost no worry of ruining the prior coat of paint
+ water color/pastel wash: very easy to use, also very forgiving too. I consider this one "fool-proof" since we only need to soak the model in water if we make a mess. However, this one is not durable and requires top-coat ASAP. This is by far my favourite method. Sometimes, I even use ink (the one that you put in students' fountain pen) - see my Zaku black tri star post
+ gundam marker/pencil: I like this one a lot since it's so easy and fast. I'm planning on using this for my next model.
But then, it all comes down personal references I think.